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rRC:SP:77-2008
MANUAL FOR DESIGNCONSTRUCTION & MAINTENANCE
OF GRAVEL ROADS
INDIAN ROADS CONGRESS2008
i
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IRC:SP:77-2008
MANUAL FOR DESIGN,CONSTRUCTION & MAINTENANCE OF
GRAVEL ROADS
Published by
INDIAN ROADS CONGRESSKama Koti Marg,
Sector 6, R.K. Puram,
New Delhi-no 022
2008
Price Rs. 400.00
(Packing & Postage Extra)
IRC :SP:77-2008
First Published : September, 2008
(All Rights Reserved. No Part of this Publication shall be
reproduced, translated or transmitted in any form or by any
means without the permission of the Indian Roads Congress)
Printed at: I G Printers, Okhla Phase-I, New Delhi- 110 020
(500 Copies)
IRC:SP:77-2008
CONTENTSPersonnel of the Highways Specifications & Standards Committee
Abbreviations vi
1. Introduction
1.1. Personnel of Rural Roads Committee 1
1 .2. Global Acceptance For Low Volume Traffic 2
1 .3. Life Cycle and Amenability to Stage Development 4
1.4. Techno-Socio-Economic Aspects 4
1.5. Influence of Environmental Conditions on Performance 5
1.6. The Problems of Local Moorums, Maintenance & Dust Control 6
1.7. Warrants for Sealing 7
1.8. Potential for Large Scale Applications and Employment Generation 7
1.9 Demonstration Projects 8
2. Design of Gravel Roads
2.1. Geometric Design Standards 8
2.2. Materials 9
2.3. Pavement Design for Gravel Roads 16
2.4 Drainage Design 25
2.5. Rehabilitation of Gravel Roads 33
3. Construction and Quality Control
3.1. Choice of Technology 35
3.2. Plant Selection and Usage 41
3.3. Sequence of Construction Operations 41
3.4. Earthwork and Subgrade Preparation 41
3.5. Sub-base Construction 43
3.6. Gravel Base/Surface Course Construction and Quality Control 48
3.7. Providing Gravel Surface 52
3.8. Sealing a Gravel Road 53
3.9. One-Coat and Two-Coat Surface Dressing 53
3.10. Step-wise Procedure for One-Coat and Two-Coat Surface Dressing 54
3.11. Step-wise Procedure for Providing 20 mm Bituminous Premix Carpet 55
IRC:SP:77-2008
4. Maintenance Methods and Management System
4.1. General 56
4.2. Surface & Structural Defects on Gravel Roads 57
4.3. Maintenance of Gravel Roads 60
4.4. Maintenance of Shoulders, Drainage and Structures 72
4.5. Special Problems of Hill Road Maintenance 74
4.6. Maintenance Management 75
4.7. Organizational Aspects of Maintenance Management 77
4.8. Do's and Don'ts 78
Appendix 2.1 79
Bibliography 84
IRC:SP:77-2008
PERSONNEL
1. (Convenor)
2. Singh, Nirmaljit
(Co-Convenor)
3. Sharma, Arim Kumar(Member-Secretary)
4. SinhaV.K.
5. Ahluwalia, H.S.
6. Bahadur, A.P.
7. Basu, S.B.
8. Chandrasekhar, B.P., Dr.
9. Datta,P.K.
10. Desai, J.P.
11. Deshpande, D.B.
12. Dhingra, S.L., Dr.
13. Gupta, D.P.
14. Gupta, K.K.
15. Jain, N.S.
16. Jain, R.K.
17. Jain, S.S., Dr.
18. Kadiyali, L.R., Dr.
19. Kandaswamy, C.
20. Krishna, Prabhat
OF THE HIGHWAYS SPECIFICATIONS ANDSTANDARDS COMMITTEE
(As on 7* November., 2007)
Add!. Director General Ministry of Shipping, RoadTransport & Highways, New Delhi
Member (Tech.), National Highways Authority of India,
New Delhi
Chief Engineer (R) S&R, Ministry of Shipping,
Road Transport & Highways, New Delhi
Secretary General, Indian Road Congress
Members
Chief Engineer, Ministry of Shipping, Road Transport
& Highways, New Delhi
Chief Engineer, Ministry of Shipping, Road Transport
& Highways, New Delhi
Chief Engineer (Pig.), Ministry of Shipping, RoadTransport & Highways, New Delhi
Director (Tech.), National Rural Roads Development
Agency (Ministry of Rural Development), New Delhi
Executive Director, Consulting Engg. Services (I) Pvt.
Ltd., New Delhi
Sr. Vice-President (Tech. Sen), Gujarat Ambuja CementLtd., Ahmedabad
Vice-President, Maharashtra State Road Development
Corporation, Mumbai
Professor, Indian Institute of Technology, Mumbai
DG(RD) (Retd.), MOSRT&H, New Delhi
Chief Engineer (Retd.),Haryana
Chief Engineer, Ministry of Shipping, Road Transport
& Highways, New Delhi
Chief Engineer (Retd.) Haryana PWD, Sonepat
Professor & Coordinator, Centre of Transportation
Engg., IIT Roorkee
Chief Executive, L.R. Kadiyali & Associates, New Delhi
Member (Tech.), National Highways Authority of India,
New Delhi
Chief Engineer (Retd.), Ministry of Shipping, RoadTransport & Highways, New Delhi
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IRC:SP:77-2008
21. Kukreti, B.P.
22. Kumar, Anil
23. Kumar, Kamlesh
24. Liansanga
25. Mina, H.L.•
26. Momin, S.S
27. Nanda,P.K.Dr.
28. Rathore, S.S.
29. Reddy, T.S., Dr.
30. Sachdev, V.K.
31. Sastry, G.V.N.
32. Sharma, S.C.
33. Sharma, V.M., Dr.
34. Shukla, R.S.
35. Sinha,A.V.
36. Srivastava, H.K.
37. Velayudhan, T.R
1 . President, Indian Roads Congress
2. Director General (Road Dev.)
3. Secretary General
1. Borge,V.B.
2. Justo, C.E.G., Dr.
3. Khattar, M.D.
Chief General Manager, National Highways Authority
of India, New Delhi
Chief Engineer (Retd.), CDO, Road Constn. Deptt.,
Ranchi
Chief Engineer, Ministry of Shipping, Road Transport
& Highways, New Delhi
Engineer-in-Chief& Secretary, Mizoram PWD, Aizawl
E-in-C/Secretary to the Govt, of Rajasthan, PWD, Jaipur
Former Member-Maharashtra Service Commission, Mumbai
Director, CentralRoadResearch Institute, NewDelhi
Secretary to the Govt, of Gujarat, Gandhinagar
Senior Vice-President, NMSEZ Development
Corporation Pvt. Ltd. Mumbai
Chief Engineer, MOSRT&H
Engineer-in-Chief (R&B), Andhra Pradesh PWD,Secunderabad
DG(RD) & AS (Retd.), MORT&H, New Delhi
Consultant, AIMIL, New Delhi
Ex-Scientist, Central Road Research Institute, New Delhi
Chief General Manager, National Highway Authority of
India, New Delhi
Director (Projects), National Rural Roads Development
Agency, (Min. of Rural Dev.), New Delhi
Addl. DGBR, Directorate General Border Roads,
New Delhi
Ex-Officio Members
(Patel, Subhash)
(Prakash, Indu) Ministry of Shipping, Road Transport&Highways, New Delhi
(Sinha, V.K.), Indian Roads Congress
Corresponding Members
(Past-President, IRC), Secretary (Roads), Maharashtra
PWD, Mumbai
Emeritus Fellow, Bangalore University, Bangalore.
Executive Director, Hindustan Construction Co. Ltd.,
Mumbai
4. Merani, N.V Principal Secretary (Retd.), Maharashtra PWD, Mumbai
(ii)
IRC:SP:77-2008
ABBREVIATIONS
AADT : Annual Average Daily Traffic
AASHTO : American Association of State Highway and Transportation Officials
ALD : Average Least Dimension
CBR : California Bearing Ratio
cm : Centimetre
CVPD : Commercial Vehicles Per Day
ESAL : Equivalent Standard Axle Load (18 kips i.e. 80 kN)
GWT : Ground Water Table
HCV : Heavy Commercial Vehicle
HFL : High Flood Level
IS : Indian Standard
km : Kilometre
m : Metre
MCV : Medium-Heavy Commercial Vehicle
MDD : Maximum Dry Density
MORD : Ministry of Rural Development
mm : Millimetre
OMC : Optimum Moisture Content
PCI : Pavement Condition Index
PI : Plasticity Index
PMC : Pre-Mix Carpet
SD : Surface Dressing
TRRL : Transportation and Road Research Laboratory ofUK
VDF : Vehicle Damage Factor
WBM : Water Bound Macadam
(iii)
IRC:SP:77-2008
MANUAL FOR DESIGN, CONSTRUCTION& MAINTENANCE OF GRAVEL ROADS
1. INTRODUCTION
1.1. The Rural Roads Committee (H-5) of the Indian Roads Congress approved theth
document in its meeting held on 9 June 2007 subject to incorporation of comments of the
members by the Sub-Group constituted for the purpose. The draft document was then finalised
by the Sub-group comprising S/Shri S.C. Sharma, RK. Katare,Dr. N.B. Lai and Shri Gurdip S.
Khinda. The personnel ofRural Roads Committee (H-5) as on 9*^ June, 2007 are as follows:
Gupta, D.R ... Convenor
Chandrasekhar, B.R Dr. ...Co-Convenor
Katare, RK. ...Member-Secretary
MembersAgarwala, S.K. Kumar, Praveen, Dr.
Baliga, Sushant Mina, H.L.
Datta, RK. Nanda, RK., Dr.
Dev, RN. Prakash, H.S.
Kadiyali, L.R., Dr. Sarkar, A.K.
Kalra, B.B. Sharma, S.C.
Kand C.V., Dr. Sharma, S.K.
Krishna, Prabhat Singh, Amrit Inder
Kumar, Ashok, Dr. Engineer-in-Chief, A.RKumar, Anil Director, HRS
Corresponding MembersJusto, C.E.G., Dr. Mitra, G.C., Prof
Singh, C.K., Dr.
Ex-Officio MembersPatel, Subhash President, IRCDG (RD), MOSRT&HSinha, V.K. Secretary General, IRC
The draft Manual finalised by the Sub-group as well as by Convenor, H-5 Committee
was placed before the Highways Specifications & Standards Committee (HSS) in its
meeting held on 7* November, 2007. The HSS Committee approved the draft with some
modifications. The modified draft document was put up before the IRC Council in its
meeting held on 16* November, 2007 at Jaipur during 68*'' Annual Session of IRC and the
Council approved the draft document for publishing as IRC document.
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1.2. Global Acceptance for Low Volume Traffic
1.2.1. Internationally, the unpaved roads (i.e. roads without bituminous or cement
concrete surfacing) constitute a sizable proportion of the total road length. In several
countries, the unpaved road length is more than the paved road length, as can be seen in
Fig. 1.1. In India, however, the unpaved road length constitutes less than half the total road
length (Fig. 1.2.). While in most countries abroad, among the unpaved roads, it is the Gravel
Roads, which are most popular, the unpaved roads in India are generally WBMsurfaced. More recently, especially with the World Bank assistance in some rural areas of In d i a
,
Gravel Roads showing good performance even after about 5 years of service have begun to earn
the confidence ofrural road engineers in the country.
UNPAVED ROAD LENGTH
17 18 PAVED ROAD LENGTH
BRAZIL SOUTH CHINA MEXICO CANADA AUSTRALIA INDIA
AFRICA
Fig. 1.1 The Unpaved to Paved Road Length Ratio in Selected Countries
(Source : CIA World Fact Book 2005)
1.2.2. As per AASHTO 'For the aggregate surfaced (Gravel) roads (used for manycounty and forest roads), the maximum traffic level considered is 100,000 ESALapplications' and "The practical minimum traffic level that can be considered for any
flexible or rigid pavement during a given performance period is about 50,000
applications". Assuming that commercial vehicles constitute about 25% of the number of
vehicles plying per day (and that the heavy commercial vehicles/trucks
constitute 20% of all commercial vehicles per day). Gravel Roads are suitable for anADT upto
200 vehicles day. Further, it implies that unless the daily traffic is of the order of about 125
vehicles per day, paved road (flexible or rigid pavement) is not justified. A recent study shows
that for traffic upto 200 vehicles per day Gravel Roads have lower maintenance costs compared
to black topped roads.
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IRC:SP:77-2008
Hofto Kong, China ^99S
Armenia 2000
Thafland 1999
Singapore 1999
KazakhsUn2000
Srt Unka 1999
Ceofgla 2000
Azertaijan 2000
Uzbekistan 1S99
Tajtkstan 1989
Turkmeflisian 1
Bhutan 1999
Japan 1999
Korea, Rep of 1993
Malaysia 1999
lussian FederaSon tSdsASSB
Pakistan 1809
ean«)lade»h 1999j U
trunei Otnnsalam I999f
New Zealand 3000
ineSa 1999
Imn, islamic Rep 199^
Fii 1999
Indonesia 1999
Nepal 1999
Samoa 199l(
PmireSla 1999
Turkey 1999
Tonga 1999
Viet Naml99?ji
Vanuatu 1999
China 1999
Philippines 2000
Cambodia SCXXt
Afghaf^slan 1999
Myanmaf 1S99
Mongo^a 2000
Korea POR 1
PNG 1999
SoK»mofl isianite 19'
100%
Sources: United Nalions and ESCAP Statistical Yearbooks, which have used datafrom Gauntry Statistical
Yearbooks. For the Russian Federation these sources were supplemented by the Europa Yearbook and World
Highways, September 1998 andfor Mia by the India Statistical Abstract 1999.
Fig 1.2 : Proportion of Paved Road in Selected Economies of tlie ESCAP Region
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IRC:SP:77-2008
1.2.3. There are several access roads providing connectivity to smaller habitations with
a traffic volume that is likely to be much lower than 200 vehicles per day. In such situations, the
most suitable and economical option that emerges is the provision of an aggregate surfaced
(gravel) road. It may be appreciated that after the current programme ofproviding all-weather
access to habitations with a population over 500 has been completed, substantial inputs will still
be required to provide all-weather access to the smaller habitations with a population less than
500, where the traffic generated would generally be of a much lower order justifying provision
ofGravel Roads as a first stage option from both technical and economic considerations.
1.3. Life Cycle andAmenability to Stage Development
1.3.1. It is also estabhshed that well-engineered Gravel Roads perform satisfactorily for low
volume traffic conditions provided theneededroutine andperiodic maintenance are attended to promptly.
For most situations, the maintenance requirements are frequent but inexpensive.As in the case ofblack -
topped roads, where bituminous surface renewals are required after about every 5 to 6 years or so
dependingon traflSc, the GravelRoads too require re-gravelling periodically. Ifthe periodic re-gravelling
requirement is attended to adesign lifeof 10 years canbe considered forpurposes ofpavementdesign. For
many low-volume traflSc conditions e.g., on Unk roads connecting habitations of relatively lower
population levels. Gravel Roads can continue to serve for long periods of time. If, however, the traffic
volume and axle loads increase to a levelbeyondthe traffic load carrying capacityofa Gravel Roadand its
serviceability level comes down close to the terminal serviceabihty level, strengthening / rehabilitation
withan overlaycanbe easilyimplementedtobring it topavedroad standards.
1.3.2. Thus, one ofthe biggest advantages of initially adopting a Gravel Road option for
low volume traffic conditions is its amenability to providing a thin bituminous surface treatment
or strengthening the pavement crust followed by black topping as may be warranted by
increased traffic. If a Gravel Road needs to be black topped as warranted by increased traffic
and environmental conditions, the bituminous surface treatment can be provided over the gravel
base after suitably preparing the surface of the existing gravel base and priming it as per
specified procedure. Where warranted by increased traffic considerations, structural
strengthening by way ofan overlay ofgravel /WBM/WMM etc. layer can be provided, treating
the existing gravel base as a lower base course or a sub base.
1 .4. Techno-Socio-Economic Aspects
1.4.1. The technical aspects of adopting a Gravel Road option for low volume rural
roads include the maximized use of the low cost locally available materials and deployment of
low-cost low-capacity equipment/plant both for construction and maintenance. Thus the
requirements of materials, plant and equipment for construction and maintenance can be
accomplished within the available resources and skills in rural areas. Since no bituminous
surface treatment is envisaged at least during the initial few years of its service life, there is no
requirement of expensive bituminous materials or the hot mix plants and equipment for manu-
facture, laying and compaction ofthe bituminous mix.
1.4.2. Studies carried out under the aegis of IRC in nine selected districts on socio-
economic impact ofrural roads show that a number ofsocial benefits (like access to education and
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IRC:SP:77-2008
health faciHty etc.) and economic benefits (improved transportation of agricultural produce,
higher yield / acre, quick transportation of perishable crops etc.) accrue from the provision of
rural roads. Social and economic benefits accrued from all-weather unpaved gravel roads are
practically the same as for black topped roads.
1,5. Influence ofEnvironmental Conditions on Performance
Gravel Roads for low volume traffic conditions in rural areas work out to be the most
suitable and economical option only under certain environmental conditions. These are:-
1.5.1. Availability of quality gravel within economic leads: Where the locally
available gravels meet the specified requirements of grading and plasticity for use in the
gravel base and surfacing as such, without any further processing, and are available
within short leads, say less than 5 to 10 km, Gravel Roads would generally work out to be the
most preferred alternative. However, where further processing by way of blending
with other local materials or by lime/cement treatment is required, the related costs
should be worked out and compared with the cost of other low-cost alternatives like paving with
bricks, stones, cement concrete blocks, as feasible. Similarly when the
distance of haulage of gravel is too long, the cost of haulage must be considered and compared
with the cost ofother alternatives.
0
1.5.2. Rainfall: High intensity ofrainfall causes high gravel loss on a gravel road as also
when the total annual rainfall is high, i.e. over 1500-2000 mm per year. However, it is more
meaningful to consider the combined effect of traffic and rainfall on the rate of
deterioration of a gravel road surface. Although no systematic performance records of gravel
roads for different amounts of rainfall are available, it is observed that under high
amount of rainfall, over 1500 mm/ year, a Gravel Road can take upto 100 vehicles per day; for
medium rainfall of 1000-1500 mm per year, a Gravel Road can take upto 150 vehicles per day
while for low rainfall less than 1 000 mm, a Gravel Road can take upto 200 vehicles per day.
1.5.3. Prolonged dry seasons: In areas with prolonged dry seasons, say 8 months or
more ofdry periods during a year, the gravel surface loses, under traffic or by wind, the very fine-
sized particles which provide the binding at the surface. As a result, dust nuisance is caused all
around the unsealed road. In such situations, it becomes necessary to use dust palliatives. If,
however, the cumulative cost ofproviding dust palliatives works out to be higher than the cost of
sealing the surface, a low cost thin bituminous surface treatment can be resorted to.
1.5.4. Longitudinal gradients: In the low rainfall regions, with less than 1000 mm/year,
the longitudinal gradients should not be steeper than 6%. Where the rainfall is in the range of
1 000 to 1 500 mm/year, the longitudinal gradients should not be steeper than 5%, provided proper
precautions are taken to prevent erosion.
1.5.5. Traffic volume: When the traffic volume is upto 100 vehicles per day, (excluding
2-wheelers), Gravel Roads are considered suitable except in case ofvery poor subgrade. Where
the traffic volume is upto 150 vehicles per day (excluding two-wheelers). Gravel Roads are
considered suitable except for the weak subgrades upto CBR of 4. For traffic upto 200 vehicles
per day (excluding 2-wheers), Gravel Roads are suitable for subgrades with CBR of5 and above.
For traffic volume above 200 vehicles per day (excluding two-wheelers). Gravel Roads are not
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IRC:SP:77-2008
considered suitable.
1.6. The Problems ofLocal Moorums, Maintenance& Dust Control
1.6.1. Local moorums: In India, the term 'Moorum' is commonly used to define soils and
gravels ofcertain types. Contrary to this belief, there is no soil group termed as 'Moorum' in the
Indian Soil Classification System or any such classification system internationally.
1.6.1.1. It is, therefore, not only desirable but necessary that moorum samples fi"om any
source and at various depths from that source must first be classified as per the Soil
Classification system before considering them for use in a Gravel Road. It may be pointed out
here that many 'moorums' do not even classify as 'Gravels' by the IS Soil Classification System; in
fact, several varieties when tested for their particle size distribution and their Liquid and Plastic
Limits, get classified as 'Clayey Sands' (SC).
1.6.1.2. As per the Indian Soil Classification system, any soil sample that has more than
half its weight retained on IS:75 micron sieve is a coarse-grained soil. Ifany coarse-grained soil
has more than half the weight of its coarse fraction retained on IS sieve of 4.75 mm size, it is a
'Gravel', denoted by the symbol "G". All Gravels are further classified as under, by the Indian
Soil Classification System:
• Well-graded Gravels GW Uniformity Coefficient>4
(Percent Fines>5%)
• Poorly-graded Gravels GP Not Satisfying GW requirements
(Percent Fines<5%)
• Silty Gravels GM(Percent Fines> 12%)
• Clayey Gravels GC(Percent Fines>12%)
As per the specified requirements, only the gravels classified as GW and GP may be suitable for
use in Gravel Base Courses whileGM an GC types are not suitable. For use in Gravel Surfacings,
GM and GC may ormay not be suitable whileGW and GP are generally unsuitable.
1.6.1.3. In view of the above, it is absolutely necessary for any Gravel Road project,
before incorporating local moorums that representative samples from each source and at
different depths be tested for their particle size distribution through standard set ofsieves and for
their liquid limit and plastic limit values. From the classification test data thus obtained, it would
be possible to classify them by the Indian Standard Soil Classification System. It is only
depending on the classification/soil groups to which the local moorums belong, that it would be
possible to decide whether these can be used as such or only after further processing in lubbase,
base or surfacing. Where further processing is required, the related costs should be worked out in
detail. Comparing the cost of local moorums after processing, with the cost of other alternative
low-cost materials like bricks, stone blocks etc, a decision may be arrived at in favour ofthe most
suitable and economical alternative
.
Below A-line of Plasticity Chart or
PK4
Above A-line of Plasticity Chart and
PI>7
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IRC:SP:77-2008
1.6.2. Maintenance and dust control
1.6.2.1. The performance of Gravel Roads is mainly dependent on the quality of
materials available for road construction, environmental conditions, proper maintenance and
available resources. The main factors for rapid deterioration of Gravel Roads include (i)
availability and suitability of gravel (ii) construction standards (iii) environmental and climatic
conditions (iv) drainage and (v) traffic. If adequate attention is not given to these factors, the
adverse effects on the performance of a Gravel Road are much more serious compared to the
performance of black-topped roads. Timely maintenance is crucial in the upkeep of Gravel
Roads. While the maintenance cost increases with traffic, still it is less compared to the
maintenance cost ofbituminous roads for low volumes oftraffic upto about 200 vehicles per day.
Gravel Roads suffer from loss ofgravel, which increases with the use ofinferior gravels and also
suffer deformation ofthe transverse profile. While deformations in the transverse profile need to
be rectified by periodic grading, excessive loss ofgravel would require frequent regravelling.
1.6.2.2. Another problem associated with Gravel Roads is the dust nuisance in low
rainfall regions, particularly when the surface gravel does not have adequate binding
properties. In many countries, dust Palliatives have been successfully used to control
dust nuisance in such situations. These aspects have been dealt with in detail in
Section 4 of this Manual. In certain situations, eventually bituminous sealing may be
warranted to overcome this problem.
1.7. Warrants for Sealing
1.7.1. Pneumatic tyred fast moving vehicles like the commercial rural vehicles damage
unprotected granular base and create dust nuisance. Also, the operating costs of such vehicles
are highly influenced by the smoothness of the road pavement. Bituminous surfacing will be
advantageous (i) where subgrade is very poor (CBR=2) and the traffic is in the range of30,000 to
60,000 ESAL applications (ii) where subgrade is poor (CBR less than 4) and the design traffic is
in the range of 60,000 to 1,00,000 ESAL applications and (iii) irrespective of the subgrade
strength, the design traffic is over 1 00,000 ESAL applications.
1.7.2. As part of the stage development strategy, it is often desirable to postpone the
provision of a bituminous surface treatment for the first few years of its service life during
which the pavement may undergo any undulations and the entire pavement system, including the
drainage system gets stabilized. Surface dressing is considered the most suitable and economical
surface treatment. It is always desirable to have some time gap between the application of first
coat and the second coat.
1.8. Potential for Large ScaleApplications and Employment Generation
1 .8.1 . In view ofthe fact that many ofour rural roads are mainly "farm to market" roads,
the design traffic is of a very low order and Gravel Roads can adequately cater to such low
volumes of traffic. After the current PMGSY targets are achieved, the remaining about 1 .7 lakh
unconnected habitations with population below 500 will generate even lower volumes oftraffic.
For such volumes oftraffic. Gravel Roads can be quite suitable.
1.8.2. The provision of Gravel Roads involving community participation can generate
tremendous employment opportunities not only for their construction but also for their
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IRC:SP:77-2008
maintenance. Furthemiore, Gravel Roads would go a long way in capacity building of small
local contractors and towards evolving appropriate technology utilizing the increasing number
of agricultural tractors for towing water bowsers and trailers, for haulage of materials, simple
implements like disc harrows for pulverization of soil clods, rotavators for blending locally
available materials and mixing ofsoil with stabilizers and water etc.
1.8.3. It is well established that the labour cost component of the total cost of the black
topped conventional pavement is much lower than the labour cost component ofthe total cost of
a Gravel Road. The construction of a Gravel Road maximises the use of locally
available materials and adoption of semi-mechanized construction techniques, thus offering
significant employment opportunities to the local communities.
Although the frequent maintenance requirements are often cited as a negative
aspect ofproviding Gravel Roads in rural areas, in fact these requirements may be considered a
big plus point in as much as they provide significant employment opportunities under various
employment generating programmes of the Central and State Governments, particularly the
National Rural Employment Guarantee Programme.
1.9. Demonstration Projects
1.9.1. Keeping in view that hardly any well-engineered Gravel Roads are being
constructed in India and that such roads are extremely popular abroad, ftill-scale
demonstration projects are warranted. If the construction and maintenance of Gravel Roads is
demonstrated in each state, such an experience would go a long way in
popularizing Gravel Roads for the low traffic volume conditions in rural areas. It is necessary to
get a feedback on the performance of well-engineered Gravel Roads, constructed under
different sets of environmental conditions. Data on road condition rating (in terms of PCI),
traffic, specific routine and periodic maintenance measures taken and their frequency should all
be recorded systematically.
2. DESIGN OF GRAVEL ROADS
2.1. Geometric Design Standards
2.1.1. Roadway width: For the single-lane gravel roads, the roadway width shall be a
minimum 7.5 m in plain and rolling terrain. However, where the traffic intensity is less than 100
motorised vehicles per day and where the traffic is not likely to increase due to
situation, like dead end etc., the roadway width shall be reduced to 6.0 m. In the mountainous and
steep terrain, the roadway width shall be 6.0 m.
2.1.2. Carriageway width: For the single-lane gravel roads, the carriageway width
shall be a minimum 3.75 m. However, where the traffic intensity is less than 100 motorised
vehicles per day and where the traffic is not likely to increase due to situations like dead end etc.
or in difficult terrain condition, the carriageway width shall be reduced to 3 .0 m.
2.1.3. Camber on carriageway: For gravel roads, the camber shall be 3.5% ( 1 in 30) for
annual rainfall less than 1 000mm and 4.0% ( 1 in 25) for annual rainfall over 1 000 mm.
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2.1.4. Crossfall on shoulders: On earthen shoulders, the crossfall should be 1%more than the camber for carriageway.
2.1.5. Longitudinal gradients: Due to the sizable proportion ofslow-moving vehicles
on gravel roads in rural areas and due to increased gravel loss on steeper gradients, it is necessary
to impose restrictions on longitudinal gradients. In plain and rolling terrain, the ruling gradient
shall be 3.5% and the limiting gradient of 5.0%, which can be relaxed upto 6%, where annual
rainfall is less than 1 000 mm. In mountainous and steep terrain, the ruling gradient shall be 5.0%and the limiting gradient of6%.
2.1.6. Horizontal alignment: The requirements of minimum radii of horizontal
curves, superelevation rates etc. for low-volume rural roads as contained in IRC:73 shall be
adopted for gravel roads. Due to the predominance ofslow-moving animal drawn cart traffic on
gravel roads in rural areas, the maximum superelevation shall be restricted to 0.07.
2.2. Materials
2.2.1. Roadmaking gravels: Roadmaking gravel has been defined as 'a mix of stone,
sand and fine-sized particles used as sub-base, base or surfacing on a road'. As per the IS Soil
Classification System,'Graver is a coarse-grained soil (with more than half the total material
coarser than 0.075 mm size), having more than halfthe 'coarse fi-action' (larger than 0.075 mm),coarser than 4.75 mm. Sand is a coarse-grained soil with more than halfthe coarse fraction, finer
than 4.75 mm. Silt and Clay are fine-grained soils with more than half the total material finer
than 0.075 mm. It is not always possible to find a suitable roadmaking gravel in a natural deposit
and often the naturally occurring gravels have to be processed to meet the specified
requirements for use in a gravel road. There are few natural deposits of material that have an
ideal gradation without being processed.
2.2.2. Grading requirements
2.2.2.1. As per the MORD Specifications, the gradation requirements of gravel/soil-
aggregate for use in base and surface courses of a gravel road are given in Tables 2.1 and 2.2
respectively. Any ofthe 3 gradings given in Table 2.1 for Base Course can be adopted depending
upon the availability ofmaterials. These gradings are recommended in case the gravel is sealed
by chip sealing or surface dressing using bituminous material.
Table 2.1 : Grading Requirements for Base Course
Sieve SizePercent by Mass Passing IS Sieve Grading Designation
A B C53 mm 100
37.5 mm 97-100 100
26.5 mm 97-100 100
19 mm 67-81 97-100
9.5 mm 56-70 67-79
4.75 nmi 33-47 39-53 47-59
425 |Lim 10-19 12-21 12-21
75 jam 4-8 4-8 4-8
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IRC :SP:77-2008
Table 2.2 : Grading Requirements for Surface Course
Sieve Size Percent by Mass Passing Designated Sieve
26.5 mm 100
19 mm 97-100
4.75 mm 41-71
425 |im 12-28
75 \im 9-16
Gravel for base courses should have very small proportion of fine materials (silt and
clay) and a relatively larger top-sized aggregate for strength and durability. Surface gravel
should have a relatively higher percentage of fines (silt and clay) and relatively smaller top-
sized aggregate, so as to readily shed offwater falling on the surface ofthe Gravel Road. Where
rounded stones are locally available, crushing ofsuch rounded stones is always suggested since
the fi-actured stones embed into the surface ofa gravel roadmuch better than rounded stones.
The percentages ofGravel, Sand and Fines (Silt and Clay) in the gradings A, B and C of
Table 2.1 are as under:
GradingA
Grading
BGrading
C
Gravel
Sand
Silt and Clay
53 to 67%
25 to 43%
4 to 8%
47 to 61%
31 to 49%
4 to 8%
41 to 53%
39 to 55%
4 to 8%
When a single naturally occurring material does not meet any of the specified
gradings, 'processing' will have to be resorted to, by blending two or more materials to achieve
the required grading.
The procedures for determining the appropriate proportioning of different materials for
achieving the prescribed grading and also to meet the requirement of Plasticity Index (PI)
have been given in Appendix-A.
2.2.2.2. Where gravel meeting the requirements in respect of grading as per the
preceding para 2.2.2.1 is not available within economic leads or cannot be economically
processed, 'Gravel' meeting the following *requirements for Base and Wearing Courses can be
used (including processing ifrequired):
(a) Base Course
Percent retained on IS 4.75 mm sieve and : 50 - 70%passing 80 mm in size
(Percent Gravel)
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IRC:SP:77-2008
Percent retained on IS Sieve 75 micron, and : 25 - 40%passing IS Sieve 4.75 mm(Percent Sand)
Percent passing IS Sieve 75 micron : Absolute max. 10%)
(Percent Slit and Clay) Desirable max. 5%)
(b) Wearing Course/Surface Course
Percent retained on IS 4.75 mm sieve and; 50 _ jqo/^
passing 80 mm in size
(Percent Gravel)
Percent retained on IS Sieve 75 micron, and . 25 - 40%passing IS Sieve 4.75 mm(Percent Sand)
Percent passing IS Sieve 75 micron . g _ ^5%(Percent Slit and Clay)
*Source : Transportation Research Board, Compendium 7 'Road Gravels'
2.2.2.3. Where gravel meeting the requirements in respect ofgrading as specified in para
2.2. 1 . and 2.2.2. is not available within economical leads or cannot be economically processed,
Soil-Aggregate mixture meeting the following requirements may be used for base and surface
courses:
Soil aggregate mixtures: Soil-aggregate mixtures may be in the form of naturally
occurring materials like soil-gravel, or soil purposely blended with suitable aggregate fractions.
The primary criteria for acceptability of such materials are plasticity characteristics and
gradation.The material should be smoothly graded for achieving the maximum possible dry
density. Fuller's grading rule {Fuller's grading rule is given by percent passing sieve = 100
(aperture size ofthe sieve/size ofthe largest particle) '} , could be used as a guide to work out the
optimum grading in different cases.A few typical gradings are given in Table 2.3. The first three
gradings indicated in this Table are especially suited for base courses whereas the remaining two
are suitable both for base course and for surfacing.
2.2.3. Plasticity characteristics offines
2.2.3.1. The requirements ofplasticity characteristics offines in surface/wearing courses
depend on the climatic conditions ofthe area. The Requirements ofLiquid Limit and Plasticity
Index offines are as under:-
Climate•
Liquid Limit(Max.)
Plasticity Index(Range)
(i) Moist temperate and wet
tropical
35% 4-9
(ii) Seasonal wet tropical 40% 6-15
(iii) Arid 55% 15-30
** Source : Low Cost Roads; UNESCO Publications. Butterworths
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IRC:SP:77-2008
Table 2.3 : Typical Grading Limits for Soil-Aggregates Mixture
Sieve Size
Percent by weight passing the sieve*
Nominal Maximum Size
80 mm 40 mm 20 mm 10 mm 5 mm80 mm 100 - - - -
40 mm 80-100 100 - - -
20 mm 60-80 80-100 100
10 mm 45-65 55-80 80-100 100
4.75 mm 30-50 40-60 50-75 80-100
2.36 mm 30-50 35-60 50-80 80-100
1.18 mm 40-65 50-80
600 micron 10-30 15-30 15-35 30-60
300 micron 20-40 20-45
75 micron 5-15 5-15 5-15 10-25 10-25
Note : Less than 10% should be retained between each pair of successive sieves specified for use
except for the pair comprising the first two sieves.
*Source : IRC : 63 - 1976
2.2.3.2. For use in base courses, the PI must not exceed 10.
2.2.4. Processing unsuitable materials: It is to be borne in mind that all types ofgravels
found in a region are not all suitable for road making, even though they classify as "Gravels" as
outlined above. In fact, there are few natural deposits that have an ideal gradation without being
processed. It is possible to take two materials, either one or both of them unsuitable alone for
highway use, and combine them to produce a granular material of satisfactory gradation. Ifthe
gradation of two available materials is known, what combinations of these materials will
produce a suitable gradation can be readily determined as per the procedure described in
Appendix-A. For many locally available materials, an effective combination may be from
crushed stone to meet the specified gradation and plasticity requirements.
2.2.5. Location and evaluation ofgravel deposits : Broadly, the procedure for location
and evaluation ofgravel deposits involves the following steps:
(a) Initial Prospecting
(i) Collect any available information in the form of Soil Maps, Geological Maps,
Aerial photographs and findings ofthe MOST Research Scheme Rl on locally
available materials in the region, local enquiries on availability ofany granular
material, rock outcrops etc.
(ii) Study any existing excavations, pits etc, and carry out a visual examination
which may warrant further investigations. Enquiries from local farmers and
residents if they have encountered any stony materials, often help in
identification ofany suitable deposits in the area.
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IRC:SP:77-2008
(iii) Study rock formations in the region. For example, in case of Igneous rocks,
any weathered granite could be a good source of gravel. In Sedimentary
rocks, there may be a possibility of gravel deposits in the form of weathered
Sand Stone and Conglomerate. Certain Metamorphic rocks with veins ofquartz
may get weathered to produce gravel. Besides, certain Limestones may lead to
the formation of calcareous aggregates like Kankar which have certain amount
of cementing action, thus showing good performance. Fig. 2.1. shows typical
quarries ofgravel.
Fig : 2.1 Typical Gravel Quarry
(b) Preliminary investigation
When the initial prospecting gives indication of possible gravel deposits at a particular
location, a number of test pits/borings should be made to demarcate the area of possible gravel
deposits. From a number ofsuch test pits/ borings, samples should be collected to determine the
quality and possible variations in the quality. For deep deposits, the variations in the quality with
depth should also be determined.A locality plan should be prepared to show the situation of the
deposit, also showing the boundaries of the deposit. The samples collected should be properly
packed and labelled (Fig 2.2). The needed laboratory tests on gradation, plasticity etc. should be
13
IRC:SP:77-2008
carried out on the samples collected. Ifthe preliminary test results so warrant, the representative
samples should be subjected to detailed investigation. It should be kept in view that the
samples not meeting the requirements ofsurface or base gravel may be suitable for use in the sub-
base courses. In order to reduce the number ofsamples for detailed laboratory investigations, it is
desirable to resort to hand-feel tests in the field.
(c) Filling in sample bags (d) Tagging and marking
Fig. 2.2 : Process of Sampling
(Source : Document on Rural Road Development in India, Vol. II, CRRI, New Delhi, 1990)
(c) Detailed Investigations
When the results of preliminary investigations for a deposit are promising, detailed
investigations should be carried out. More test pits/borings need to be made on a grid system, the
spacing depending on the variability of the deposit as determined during preliminary
investigations. In each test pit/boring, the depth ofoverburden and variations in quality ofgravel
with depth should be determined. If there are variations in quality with depth, the aspect of
mixing of materials from different depths must also be considered. Further testing work should
be carried out depending on the variations in the gravel quality from the specified requirement.
The detailed investigations will be useful in estimating the quantity of gravel available, the
overburden required to be removed and variations in the quality of gravel. Other aspects to be
looked into are the work required on clearance, the haul distance to the site of work and
availability ofaccess roads for hauling the gravels to the site.
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IRC:SP:77-2008
2.2.6. Materials sampling: It is most important to get a truly 'representative'
sample to the Laboratory for testing. The main problem in getting a 'representative' sample of
aggregate/gravel is the problem of segregation. At the stockpile, there will be a tendency for the
bigger particles to roll down towards the base. It is, therefore necessary to collect samples close
to the top, middle and bottom of the stockpile (Fig. 2.3) taking care that a wooden board should
be shoved in before collecting the samples, to prevent further segregation. All the three samples
thus collected should be mixed together and the final sample for laboratory testing, reduced by
the process of 'Quartering'. Alternatively riffle box may be used to reduce total mixed sample to
the 'representative' sample for laboratory testing.
Fig. 2.3. : Sampling from Flat Stockpiles
2.2.7. Methods of testing : The standard tests commonly used to determine the
suitability of a sample of gravel as a pavement material include the following:
(i) Particle size Distribution (18:2720 Part 4)
(ii) Plasticity Index (18:2720 Part 5)
(iii) CBRTest(IS:2720Partl6)
(iv) WetAggregate Impact Value (18:2386 Part 4)
2.2.8. Handling gravel : From the time gravel is taken fi-om the quarry, the following
should be kept in view while handling gravel:
(i) Remove the topsoil or any vegetation fi-om the surface of material source before
beginning to process the materials.
(ii) Since variations in the layers of gravel are common, it is a good practice to remove
the material by working a broad area ofthe face.
(iii) To avoid the problem ofsegregation, stockpiles should be constructed in layers.
(iv) Hauling and spreading gravel should be treated as a work zone and suitable
precautions shall be taken for safety ofworkers and road users.
(v) After gravel is dropped on the road, the grader operator should place it in a
windrow.
(vi) For a new road, prior to laying gravel on a soil subgrade, the subgrade should be
properly compacted and finished to the required profile.
2.2.9. Components ofsoil-aggregate mixtures/gravels
Various constituents of Soil-Aggregate Mixtures forming gravels and their contribution
to the strength ofthe matrix are as under
(i) Gravel and Crushed Stone : Mechanical interlock and internal friction
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IRC:SP:77-2008
(ii) Coarse Sand
(iii) Medium and Fine Sand
(iv) Silt
(v) Clay
Internal friction, reduces shrinkage
Filler with slight capillary action
Adds to capillarity, produces apparent
cohesion
Low permeability; true cohesion; causes
shrinkage
2.2.10. Soil-aggregate and water interaction: Ideally, the rate of upward suction of
water from ground water below should balance the rate of evaporation from the road surface. Atypical cross-section of a Gravel Road is shown in Fig 2.4. The water interaction in the various
layers ofa gravel road can be described as under.
Layer Water Interaction
(i) Water-resisting gravel surfacing
(ii) Base course of gravel
(iii) Sub-base and subgrade
Sheds off rainwater
Utilizes suction
Conduct water to the base course
GRAVELSURFACING
SUBGRADE
GRAVEL SURFACrVG - AWELL BOUND WATER RESISTING TREATMENT ON THE SURFACE OF THE BASE
BASE COURSE - THE MAIN GRAVEL SUPPORTING THE PAVEMENT LOADINGSUB BASE -AN OPTIONAL GRANULAR LAYERSUB GRADE - 300 mm Thick Select Soil
Fig. 2.4 : Typical Cross-Section of a Gravel Road Pavement
2.2.11. Treatment with lime/cement: Under certain conditions, it is advantageous to
improve the properties of soils and aggregates by adopting soil stabilisation techniques with
small quantities of quick/slaked lime or Portland Cement. Clay soils are improved by mixing
with lime, resulting in increased strength/CBR, reduced swelling and shrinkage characteristics,
reduced water content in natural soil, better workability and improved draining properties.
Addition ofa small amount ofcement imparts cohesion between particles ofgravels and
sands. Cement can be effectively used to upgrade poor quality gravels and sands.
2.3. Pavement Design for Gravel Roads
2.3.1. General: Basically, the methodology to be adopted for the pavement design of
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IRC:SP:77-2008
Gravel Roads is the same as given in IRC:SP:72 'Guidelines for the Design of Flexible
Pavements for Low Volume Rural Roads' except that gravel/ aggregate-surfaced roads are
provided only for very low volumes oftraffic. As per this method, the design parameters include
(i) Traffic in terms ofthe number ofstandard axles (80 kN) to be carried over the design life and
(ii) Subgrade strength in terms ofCBR. These parameters are discussed in paras 2.3.3 and2.3.4.
2.3.2. Design criteria: The thickness of gravel/aggregate-surface roads shall be based
on the following criteria:
(i) the serviceability loss over the design life is limited to 2.0, taking the initial
serviceability index to be 4.0 just before opening the road to traffic, and the terminal
serviceability of 2.0 when rehabilitation will be due, with or without provision ofan
overlay.
(ii) the allowable depth ofrutting under 3 m straight edge shall not exceed 50 mm.
2.3.3. Computation of design traffic
2.3.3.1. Seasonal variations in traffic: Most ofthe rural roads being essentially farm-to-
market roads, there are significant variations in traffic volumes as observed during non-
harvesting and harvesting seasons. The seasonal variations are shown in Fig. 2.5, typically for 2
harvesting seasons ofequal duration during a year. The Annual Average Daily Traffic (AADT),
duly accounting for seasonal variations can be determinedby the simple formula given below:-
365
Where,
T = Number ofvehicles per day, including both motorized and non-motorized,
but excluding all two-wheelers, during the lean non-harvesting season.
t = Duration ofa harvesting season in days
n = Number of times by which the number of vehicles per day 'increase at the
peak harvesting season, over and above the lean season traffic T.
The values of T and n in the above formula are often readily available from local
authorities.
The use ofthe above formula is illustrated by the following example
:
Example : (i) Lean season traffic (T) = 50 vehicles per day
(ii) Duration ofa harvesting season (t) = 40 days
(iii) Traffic at the peak harvesting season increases by 5 times (i.e, n=5) to
250 vehicles per day over and above the lean season traffic of 50
vehicles per day, i.e. a total of 300 vehicles ply per day at the peak
harvesting season.
1.2 (nxT)xtAADT = T+
365
x:
"365= 5o^'-2(5x50)x40 ^
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IRC:SP:77-2008
I I I I I I I I I I I I I I I I I I ] \ I I I I I
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jon
MONTH OF THE YEAR
Fig. 2.5 : Seasonal Variations in Traffic on Rural Roads
2.3.3.2. For upgradation of existing roads: For the upgradation of an existing rural
road, ideally, the traffic census should be conducted over a period of atleast 3days, both during
the peak harvesting season and also during the lean season. However, ifthe values of t and n can
be obtained from local authorities with reasonable reliability, traffic census during the lean
season only will suffice; for lean season traffic, local enquiries can also help.
2.3.3.3. For new roads: In case of a new road, an approximate estimate should be made
of traffic that would ply on the road, considering the number of villages and their population
served along the road alignment and other socio-economic parameters. Traffic counts can be
carried out on an existing road in the vicinity with similar conditions and knowing the population
served as well as agricultural produce to be transported, the expected traffic on the new proposed
road should be estimated. Due consideration should be given to the 'Diverted' and 'Generated'
traffic anticipated as a consequence ofthe development ofthe proposed road, land use ofthe area
served, the probable growth oftraffic and the design life.
2.3.3.4.Traffic parameters for gravel base thickness design: For purposes of
pavement design, only commercial vehicles with a gross laden weight of 3 tonnes or more along
with their axle loading are considered. These include the following:
• Heavy Commercial Vehicles (HCV) comprising heavy trucks and full sized
buses.
• Medium-Heavy Commercial Vehicles (MCV) comprising medium-heavy
trucks, mini buses, tractor-trailers, pick-up vans etc.
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IRC:SP:77-2008
The design traffic is computed in terms ofcumulative number ofstandard axles of 80 kNto be carried during the design life ofthe road, using the following formula:
N = T x365x(l + O.Olry -1
Where,''''
X L X F
N = Cumulative number of standard axles for design of gravel base
thickness
T = Number of commercial vehicles per day in the year of opening the
road
r = Annual growth rate oftraffic
L = Lane Distribution Factor = 1 for single lane/ intermediate lane
n = Design Life in years
F = Vehicle Damage Factor
The parameters F, r and n are discussed in the following paras.
2.3.3.5. Vehicle damage factor: The Vehicle Damage Factor (F) is defined as the
"Equivalent number of standard axles per commercial vehicle". While the factor 'F' is arrived at
from actual axle load surveys on the existing roads, the project size and traffic volume in the case
ofrural roads may not warrant conducting an axle load survey. Therefore, indicative F values for
HCV and MCV shall be taken as 2.5 and 0.33 respectively when fiilly laden and 0.3 and 0.02
respectively when unladen. In many situations information regarding laden and unladen
commercial vehicles may not the available. The following VDF values shall be used for design
purposes, where actual data is not available:
Vehicle Type Vehicle Damage Factor
HCV 2.0
MCV 0.3
2.3.3.6. Traffic growth rate: The traffic growth rate depends upon the potential of an
area for generating traffic. In the absence ofany reliable information on this aspect, a 6% growth
rate (r) shall be taken for design purposes. The same annual growth rate of traffic shall be
considered from the year when actual field traffic surveys were carried out to the year ofopening
the road to traffic.
2.3.3.7. Design life: Normally, the gravel base thickness requirement shall be worked out
for a design life (n), of 10 years. However, depending on factors, such as the limited availability
offunds, a lower design life, not less than 5 years, shall be adopted.
2.3.3.8. Estimating design traffic parameters: In the absence of adequate data in
respect of commercial vehicles and proportions of HCV and MCV, a reasonable estimate of
design traffic in terms of cumulative standard axles during the design life of a gravel road shall
be obtained as under:
AADT* Cumulative ESAL AppUcations For 10-Year
Design Life
50 10,000
100 50,000
150 75,000
200 100,000
Includes both motorized and non-motorized vehicles, except two-wheelers.
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IRC:SP:77-2008
While pneumatic tyred carts do not need to be considered for purposes of pavement
design, it is always desirable to consider the effect of solid-wheeled (iron-rimmed)
carts in estimating traffic for pavement design. For this purpose, the correction factor
given in para 3.4.6 of IRC:SP:72-2007 shall be applied.
2.3.3.9. Traffic categories: For pavement design of gravel roads, the traffic has been
divided into three categories as under:
Traffic Category Cumulative ESAL Applications (N)
T. 10,000-30,000
30,000-60,000
T3 60,000-100,000
2.3.4. Subgrade strength
2.3.4.1. Design for new roads
2.3.4.1.1. SubgradeCBR value
For the pavement design of new roads, the subgrade strength needs to be evaluated in
terms ofCBR value.
The CBR tests should be conducted on representative samples of subgrade soil
compacted by static compaction to 100% Standard Proctor dry density and tested at a moisture
content corresponding to the wettest moisture condition likely to occur in the subgrade during its
service life. An average of test values obtained from a set of 3 specimens should be reported. If
high variations are observed in the test values from the set of3 specimens, then an average oftest
values obtained from 6 specimens should be taken.
2.3.4.1.2. Selection ofmoisture content for subgrade strength evaluation
The subgrade moisture conditions can be classified as under:-
Subgrade Classification Estimate Subgrade Moisture Content
I. Where the GWT is close enough to the
ground surface to influence the subgrade
moisture content. In non-plastic soils, GWTwill influence the subgrade moisture
content, if it rises to within Im of the road
surface; in clays oflow plasticity (PI<20), if
GWT rises within 3 m of the road surface
and in heavy clays (PI<40), if GWT rises
within 7m ofthe road surface. This category
also includes coastal areas and flood plains
where the GWT is maintained by the sea, by
a lake or by a river, besides areas where
GWT is maintainedby rainfall.
1 . The most direct method is to measure the
moisture content in subgrades below
existing pavements in similar situations at
the time of the year when the GWT is at its
highest level.
2. The subgrade moisture content for
different soil types can be estimated by
using the ratio
Subgrade Moisture Content
Plastic Limit
which is about the same when GWT and
climatic conditions are similar.
3. Where such measurements are not
possible, the subgrade strength may be
determined in terms of 4-day soaked
CBR value.
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IRC:SP:77-2008
II. Subgrades with deep GWT but where
seasonal rainfall brings about
significant changes in moisture
conditions under the road.
The subgrade moisture condition will
depend on the balance between the water
entering the subgrade through pavement
edges/shoulders during rains and the
moisture leaving the ground during dry
periods. The design moisture content can
be taken as optimum moisture content
obtained from Proctor Compaction Test
IS:2720 (Part 7) corresponding to
maximum dry density.
The Possibility oflocal perched GWTand effects of seasonal flooding should,
however, also be considered while
deciding on GWT depth. Where such
situations are encountered, the subgrade
strength may be determined in terms of
4-day soakedCBR value.
2.3.4.1.3. The Soaked CBR value ofthe subgrade can be determined by conducting CBRtests on 4-day soaked samples in the laboratory. Where adequate testing facility is not available,
typical presumptive values given in Table 2.4 can be adopted. Alternatively, soaked CBR value
can be estimated using theNomograph given in IRC :SP :72
.
Table 2.4 : Topical Presumptive Design CBR Values
Description of
Subgrade SoilIS Soil
Classification
Typical SoakedCBR Value (%)
Highly Plastic Claysand Slits
CH, MH * 2-3
Silty Clays andSandy Clays
ML, MICL, CI
4-5
Clayey Sands andSilty Sands SC, SM 6-10
Expansive clays like BC soil may have a soaked CBR of less than 2%
A simple Free Swelling Index test (IS:2720 Part 40) should be determined on
expansive clays
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IRC:SP:77-2008'
2.3.4.2. Upgradation/rehabilitation of existing roads: The insitu subgrade strength of
an existing road will be determined in terms ofCBR value obtained on representative subgrade
soil samples remoulded to the insitu density at the field equilibrium moisture content, observed
after the recession of the rainy season. If, for some reason, it is not found possible to determine
the field moisture content immediately after the recession ofmonsoon, the 4 days' soaked CBRvalue of the remoulded subgrade soil samples, compacted at field moisture content to field
density, may be determined.
2.3.4.3. Subgrade strength classes : In order to use the Design Chart (Para 2.3.5), the
subgrade strength is divided into the following classes:
Quality of
SubgradeClass
Range(CBR%)
Very Poor* SI 2
Poor S2 3-4Fair S3 5-6Good S4 7-9
Very Good S5 10-15
* Where the CBR of subgrade soil is less than 2, the economic feasibility of replacing
300 mm subgrade with suitable soil needs to be explored and, if found feasible, the
pavement should then be designed based on the CBR value ofthe improved subgrade.
Alternatively, a capping layer ofthickness not less than 100 mm ofmodified soil (with
CBR not less than 1 0) should be provided.
2.3.5. Design chart: The gravel base thickness required for the five subgrade
strength classes (S,, Sj, S3, S4 and S5) and for the traffic categories ofcumulative ESAL repetitions
10,000-30,000 (T,); 30,000-60,000 (T^) and 60,000-100,000 (T3) are shown in Fig. 2.6. Achart
to convert a portion ofthe Aggregate Base Layer thickness to an equivalent thickness ofsubbase
(MORD Specifications Clause 401) with an intermediate CBR value between the base and
subgrade is shown in Fig. 2.7. It must, however, be ensured that a minimum 1 00mm thickness of
gravel base is always provided. Besides grading requirements specified for gravel base and
surfacing, the minimum soaked CBR of 80 for the gravel base material is often considered an
additional requirement. It must be kept in view that ifthe gravel base material does not meet any
ofthe two requirements (viz grading and soaked CBR value), it may not be able to withstand the
design cumulative ESAL applications over the design life, consequently requiring regravelling
earlier than designed. It may also be pointed out here that for the recommended designs to
perform satisfactorily over the design life, it is implied that all the needed routine and periodic
maintenance inputs will be provided.
2.3.6. Surface gravel: The thicknesses provided in the Design Catalogue (Fig. 2.6) are
the Gravel base thicknesses and the base gravel conforms to the requirements given in para 2.2.
Base Gravel may not form a durable crust to keep the material bound together on a Gravel Road
and is difficult to maintain. It is, therefore, recommended that the gravel base shall be covered
with the surface gravel material conforming to para 2.2. The thickness of the surface layer will
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IRC:SP:77-2008
generally vary from 40 to 50 mm depending on the traffic and quality ofmaterial. In some cases,
a running course comprising a thin loose layer ofapprox. 1 3 mm size gravel or crushed aggregate
has been provided over the surface course, acting as a cushion between the wheel load and the
pavement surface. In India, there has not been enough experience with such a running course and
should first be tried out on an experimental basis.
CUMULATIVE ESAL APPLICATIONS
SUBGRADE STRENGTH(CBR) 10,000 TO 30,000 30,000 TO 60,000 60,000 TO 1,00,000
VERY POOR(CBR = 2)
200
100
75
150
100
75
100
100
100
POOR(CBR = 3 to 4)
200275
75
100
150
FAIR(CBR = 5 to 6)
175250 275
GOOD(CBR = 7 to 9)
150 , 175 225
VERY GOOD(CBR = 10 to 15)
125 150 175
NOTE: IN SITUATIONS WHERE LOCALLY AVAILABLE/SUITABLY PROCESSED GRAVEL BASE MATERIAL FULFILLSALL REQUIREMENTS AND THEENGINEER IS SATISFIED THAT THE GRAVEL BASE MATERIAL IS WELLCOMPACTED, THE TOP 75 mm WBM LAYER MAY BE DISPENSED WITH, FOR CUMULATIVE TRAFFICUPTO 1,00,000 ESALAPPLICATIONS.
LEGEND
Dmmi
BITUMINOUS SURFACE TREATED WBM/CRMB
BASE OF GRAVEL/CRMBAVBM; CBR NOT LESSTHAN 100 (WHERE 100 mm THICKNESS IS)
RECOMMENDED, IT MAY BE MODIFIED TO 75 mmTHICKNESS FOR WBM CONSTRUCTION, WITHCORRESPONDING INCREASE OF 25 mm INSUBBASE THICKNESS).GRAVEL BASE(CBR NOT LESS THAN 80; IN EXCEPTIONAL CASES)MAY BE RELAXED SUITABLY)GRANULAR SUB-BASE(CBR, NOT LESS THAN 20; IN EXCEPTIONAL)CASES MAY BE RELAXED TO 15)
MODIFIED SOIL/IMPROVED SUBGRADE(CBR, NOT LESS THAN 10)
Fig 2.6 : Pavement Design Catalogues
23
IRC:SP:77-2008
Example:
Initial Base Thickness DBSi = 27.5 cmFinal Base Thickness DBSf = 15.0 cmSubbase CBR = 30
Base CBR = 100
Solution : Subbase Thickness required = 2Qbm
Required Subbase Thickness, DSB (cm)
Fig. 2.7. Chart to convert a portion of the Gravel/Soil-Aggregate Base Layer
Thickness to an Equivalent of Subbase
(Adapted From : AASTHO Guide for Design of Pavment Structures, AASHTO, 1993)
24
IRC:SP:77-2008
2.4. Drainage Design
§
2.4.1. Principles of good drainage: Since water is, beyond doubt, one of the critical
factors causing failure ofroads, the designer should aim at keeping the water away from the road-
bed. This can be achieved by following some simple principles of drainage design. They are
outlined below:
(i) The surface nin-offover the pavement surface and the shoulders should be drained
away as quickly as possible, preventing the water from finding entry into the
pavement layers from the top and into the subgrade from the top and sides
.
(ii) Precipitation over the open land adjoining the highway should be led away from the
road through natural drainage channels or artificial drains. Suitable cross-drainage
channels should be provided to lead the water across the road embankment which
may be cutting across to the natural drainage courses.
(iii) Consideration should be given to deal with the precipitation on the embankment
and cut slopes such that erosion is not caused.
(iv) Seepage and sub-surface water is detrimental to the stability of cut slopes and
bearing capacity of subgrades. An effective system of sub-surface drainage is a
guarantee against such failures.
(v) Landslide-prone zones deserve special investigations for improving drainage.
(vi) Poor embankment soils can perform satisfactorily if drainage is considered in the
design.
(vii) Water logged and flood-prone zones demand detailed consideration for improving
the overall drainage pattern ofthe area through which the road is aligned.
2.4.2. Longitudinal gradient: Despite the provision of adequate cross-slopes, slight
longitudinal drainage is necessary.Aminimum 0.3% longitudinal gradient is to be ensured.
2.43. Cross slope/camber: As specified in para 2.1.3, the crossfall/camber over the
carriageway for gravel roads should be 3.5% for low rainfall areas and 4.0% for high rainfal areas.
2.4.4. Shoulder drainage : For an efficient and quick drainage of rain water from the
roadway, it is necessary to ensure that the shoulder surface is properly sloped and is free from any
depressions or irregularities in the surface, where rainwater could get trapped.
On earthen shoulders, the crossfall should be Wo more than the camber for carriageway
(refer para 2. 1.4).
2.4.5. Roadside drains
2.4.5.1. Computation ofrun-off : All the rainfall which falls on the catchment area does
not reach the point where the drainage facility is being designed. This is due to percolation and
evaporation losses, which are governed by factors such as soil type, vegetative cover, steepness
of slope of the catchment, length of travel, temperature, land-use etc. The following formula.
25
IRC:SP:77-2008
known as the Rational Formula, is generally used for calculation ofrun-off:
Q = 0.028 PI,A
Where,
Q = Maximum run-oflfincumper second
P = Aconstant depending upon the nature ofsurface
= Critical intensity of storm in cm per hour occurring during the time of
concentration
A = Catchment area in hectares
The value ofP is given in Table 2.5
Table 2.5 : Values of Coefficient of Run-off
S.No. Description of SurfaceCoefficient of
Run-off (P)
1.Steep rock and watertight pavement surface
(concrete or bitumen)0.90
2. Steep rock with some vegetative cover 0.80
3. Plateau areas with light vegetative cover 0.70
4. Bare stiff clayey soils (impervious soils) 0.60
5. Stiff clayey soils (impervious soils)
with vegetative cover and uneven paved road surfaces
0.50
6. Loam lightly cultivated or covered andmacadam or gravel roads.
0.40
7. Loam lightly cultivated or covered andmacadam or gravel roads.
0.30
8. Sandy soil, light growth, parks, gardens,
lawns and meadows0.20
9. Sandy soil covered with heavy bush or
wooded/forested areas0.10
2.4.5.2. Design of cross-section of roadside drains: When natural channels for
discharging the run-off are not available, it becomes necessary to design and construct artificial
channels. Examples ofsuch channels are:
( 1 ) Side drains in cut-sections
(2) Catchwater drains or Interceptor drains
(3) Longitudinal drains along the edge of embankment to lead run-off water to
natural channels/roadside drains /ditches
The three main types ofcross-sections for roadside drains/ditches are shown in Fig. 2.8.
Of the three shapes, the parabolic section is hydraulically the best and least subject to erosion,
even though not as easy in construction as the triangular and trapezoidal shapes. The triangular
section, although easy to construct is very much susceptible to erosion and gets easily blocked
with debris. The most commonly used cross-section is the trapezoidal section as it is acceptable
fi-om both considerations-hydraulic as well as ease ofconstruction. The side slopes should not be
steeper than 2:1, firom the view point of ease in grassing. The bottom width should normally be
not less than 0.3 m.
26
IRC:SP:77-2008
TRAPEZOIDAL
Fig. 2.8 Main Types of Cross-Section
27
IRC:SP:77-2008
For gravel roads, a return period ofone year is to be adopted in estimation ofrun-off For
design purposes, the storm duration should be chosen equal to the 'time of concentration'
based on the assumption that maximum discharge at any point in a drainage system
occurs when the entire catchment is contributing to the flow. The 'time ofconcentration' far from
any watershed is 'the time required for a given drop of water from the most remote part of the
watershed to reach the point ofexit' and comprises oftwo components (i) entry time and (ii) time
of flow (see Fig. 2.9). If the drainage point under consideration is at the entry of the drainage
system, then entry time is the time of concentration. If, however, the drainage point is situated
elsewhere, then time of concentration is the sum of the entry time and the time required to
traverse the length of the point under study. Fig. 2.10 gives a graph for estimating time of
concentration for catchement for different lengths, character and slope.
It is to be recognized that shorter the duration of critical rainfall, the greater would be the
expected average intensity during that period. For example, during a 60 minute rainfall,
some 10 minute period will have an average rainfall intensity far greater than for the
whole storm.
For very reliable estimation of critical intensity of rainfall, it would be ideal to have the
rain gauge records available at short intervals say 5, 10, 20, 30, 40, 50, 60 minutes.
Alternatively, the following equation can be used.
F(T+1)1 ~ T(t+1)
Where,
I = intensity ofrainfall within a shorter period of t hours within a storm
F = total rainfall in a storm in cm falling in duration ofstorm of T hours
t = smaller time interval in hours within a storm duration of T hours
The one-hour rainfall maps of India for return periods of 2, 5, 10, 25 and 50 years are
available.
For built-up areas, an entry time (or inlet time) of 5 to 1 0 minutes is normally used, but in
the case of grassy plots it may take 10 to 20 minutes for water to flow over a distance of 30 m.
This factor decreases in importance as the length ofdrain increases and entry time (or inlet time)
becomes a small proportion of the time of concentration. For a quick estimation of time of
concentration. Fig. 2.10 can be used.
The hydraulic design ofsuch channel is usually done on the basis ofManning's formula:
n
Where,
V = Velocity inm per second
R = Hydraulic mean depth
S = Bed slope
n = Rugosity coefficient
28
IRC:SP:77-2008
Remotest Pointf or oreo A
Remotest point
for oreo 6
Entry timeCt)
from (4) to (3)
Areo A
'0Drain
Areo B
s\N
®
Entry time (ti)
from ® to (?)
Flow fimeCti)
from (D to (Din drain
Fig. 2.9 : Time of Concentration
Smooth 0''*Ch Bora Poor Av«ro<povement section soii turf tu,(
Tim? ot concentrotion (minutes)
Fig. 2.10 : Chart of Estimating Time of Concentration (IRC:SP:42)
29
IRC:SP:77-2008
The values ofn are given in Table 2.6.
The discharge Q is then worked out using the equation:
Q=AV
Table 2.6 : Manning's 'n' And Maximum Permissible Velocity of
Flow in Open Channels
S.No. Ditch Lining Manning's 'n' Allowable velocity to
prevent erosion m/s
(1) (2) (3) (4)
1. Natural Earth
A. Without Vegetation
(i) Rock(a) Smooth and Uniform 0.035-0.040 6
(b) Jagged and irregular 0.04-0.045 4.5-5.5
(ii) Soils (Extended Casagrande classification)
V Iw U.UZZ-U.UZ<4 1 .o-Z. 1
GP 0.023-0.026 2.1-2.4
GC 0.020-0.026 1.5-2.1
GM 0.024-0.026 1.5-2.1
sw 0.020-0.024 0.3-0.6
SP 0.022-0.024 0.3-0.6
sc 0.020-0.023 0.6-0.9
SM 0.023-0.025 0.9-1.2
CL and CI 0.022-0.024 0.6-0.9
MI and ML 0.023-0.024 0.9-1.2
OL and OI 0.022-0.024 0.6-0.9
CH 0.022-0.023 0.6-0.9
MH 0.023-0.024 0.9-1.5
OH 0.022-0.024 0.6-0.9
Pt 0.022-0.025 0.6-0.9
B. With vegetation
(i) Average turf
(a) Erosion resistant soil 0.050-0.070 1.2-1.5
(b) Easily eroded soil 0.030-0.050 0.9-1.2
(ii) Dense turf
(a) Erosion resistant soil 0.070-0.090 1.0-2.4
(b) Easily eroded soil 0.070-0.050 1.5-1.8
(c) Clean bottom wit h bushes on sides 0.050-0.080 1.2-1.5
(d) Channel with tree stumps
No sprouts 0.040-0.050 1.5-2.1
With sprouts 0.060-0.080 1.8-2.4
(e) Dense weeds 0.080-0.012 1.5-1.8
(f) Dense Brush 0.100-0.140 1.2-1.5
(g) Dense willows 0.150-0.200 2.4-2.7
2. Paved
A. Concrete with all surfaces. Good or Poor
(i) Trowel finished 0.012-0.014 6
(ii) Float finished 0.013-0.016 6
(iii) Formed, no finish 0.014-0.016 6
B. Concrete bottom, float finished, with sides of
(i) Dressed stone in mortar
(ii) Random stone in mortar 0.015-0.017 5.4-6
(iii) Dressed stone or smooth concrete rubble 0.017-0.20 5.1-5.7
(Rip-rap) 0.020-0.025 4.5.
(iv) Rubble or random stone (Rip -rap)
C. Gravel bottom with sides of 0.025-0.030 4.5
(i) Formed concrete
(ii) Random stone in mortar 0.017-0.020 3
(iii) Random stone or rubble (Rip-rap) 0.020-0.0238 2.4-3
D. Brick 0.023-0.033 2.4-3
E. Bitumen (Asphalt) 0.014-0.017 3
0.013-0.016 5.4-6
30
IRC:SP:77-2008
2.4.6. Surface drain linings
2.4.6.1. The need: Unlined, bare earth surfaces ofroadside ditches are highly susceptible
to erosion unless the flow is limited to a very small amount. It is, therefore, necessary that
roadside ditches are provided with protective lining which would avoid serious erosion
problems and keep them serviceable. There is a wide variety of different types of linings and the
choice of appropriate lining will depend on the site conditions. The most conmion lining which
works satisfactorily in most situations is grass.
2.4.6.2. Turfing: Grass lining is more economical than other linings to establish and with
proper maintenance, will provide adequate protection against erosion for most of the site
situations. A key factor to the success of grass lining is that it must form a firm, dense turf. For a
rapid establishment, of a vegetal lining in ditches, the same principles must be followed as
adopted for providing a vegetal protection cover on slopes. In the rainy season and in high
rainfall areas where it may be difficult to hold seeds and mulch in the ditch, an open mesh matting
of suitable material may be used instead of straw or hay mulch. The matting is laid down after
seeding and pegged with staples. Where more than one width ofmatting is required, as is usually
the case, the adjacent stripes should be overlapped (50-75 mm) and stapled at 2 to 2.5 m intervals.
It is important to ensure that matting is, elsewhere, in contact with the soil for, ifwater gets under
the matting, the seeds and soil will wash away. The efficiency of this technique depends on
making the water flow over the net, as it is matting which prevents erosion until vegetation is
established even when large amounts of rainwater flow over it. The roadside ditch can also be
lined with sod freshly cut, to a depth of about 20 mm fi*om a well established dense turf. Sod
strips should be placed across the ditch rather than length wise. The joints should be staggered
and strips pressed firmly against one another. After the sod is in place, it is tamped or rolled to
produce a smooth continuous surface. It should be watered for several weeks after placing, as
conditions may warrant.
2.4.6.3. Paved linings: Experience has shown that under two extreme site conditions on
very flat grades and then again on steep grades, the technique ofproviding grassing as a surface
lining does not always prove satisfactory. On very flat grades (less than 0.5 per cent), the flow
over a grass lining is too slow, giving rise to the problem of silting or occurrence of deposition
which is rather difficult to maintain, and, over steep grades, erosive velocities are reached,
which, due to the scouring action, can destroy the grass lining completely.
In these situations, alternative lining of cement concrete, brick/rubble masonry
especially on the internal streets passing through a village may be resorted to.
A practical concrete lining is the prefabricated type. In this construction, the panels are
cast in standard forms at a convenient central plant (Fig. 2.11).
2.4.6.4. Velocity of flow: For efficient functioning of a side ditch, the flow must be fast
enough to prevent silting or deposition but at the same time the flow must not be so fast as to
cause serious damage by scouring action. Ditches with grass lining should have a slope at least
0.5% to avoid deposition and siltation. The ditch has to have a grade steeper that ofthe roadway.
The ditch, in that case, will have to be deeper as it moves down grade and will also move farther
away fi-om the central line ofthe road, ifthe side slopes are not changed. One alternative way to
overcome the problem of silting or occurrence of deposition is to provide a secondary smaller
31
IRC:SP:77-2008
channel ofV shape at the bottom ofthe ditch (Fig. 2.12) to concentrate low flow in a smaller area
of cross-section thereby increasing the flow velocity. This secondary channel sustained flow
over long periods makes it impossible to maintain grass lining, a halfpipe section may be placed
in the secondary channel.
Fig. 2.11 : Prefabricated Concrete Lining
- to be grass lined
Fig. 2.12 : Secondary Channel
2.4.7. Step-wise procedure for design of open drains: The design of the channel is
done in the following step-by-step manner.
(1) From the known soil type, arrive at the value of Manning's Rugosity
coefficient, side slopes and the maximum permissible velocity.
(2) Determine the slope from the topography.
(3) For the given discharge, calculate the hydraulic mean depth from Manning's
Formula.
(4) Find out the cross-sectional area from the given discharge and the maximumpermissible velocity.
(5) From the results of steps 3 and 4, solve the simultaneous equations to obtain the
bottom width and depth.
32
IRC:SP:77-2008
2.4.8. Illustrative example: A longitudinal channel with a trapezoidal cross-section is to
be constructed in a cut section. The longitudinal slope is 1 in 250. The soil is clay, with
Mannings's Rugosity Coefficient of0.024. The maximum allowable velocity is 0.6 m/s. Designthe drain for a discharge of 0. 1 cum/s.
j:;^2/3g1/2
Solution V=
7?''^ (0.004)0.6 =
1/2
0.024
^ 0.6x0.024
0.063 ,
Discharge Q = 0.1=VxA = 0.6A
R =
V
0.024
= 0.12m
A =OA
0.6= 0.16
Perimeter P =0.16
= 1.3 mR 0.12
Taking the side slopes of the trapezoidal drain as 2 horizontal : 1 vertical
P = b+2d(l+2y = b+4.48d=1.3
Where b is the base width ofthe drain and d, the depth in metres. For a drain base width of0.3 m,the depth works out to about 0.22 m. A typicalcross-sectionofthedrainisshownin Fig.2.13
Fig. 2.13 : Typical Cross-Section for Illustrative Example
2.5. Rehabilitation of Gravel Roads
2.5.1. Rehabilitation factors: The various factors to be considered for rehabilitation
are as under :-
• Whether an overlay/strengthening layer is required or a non-overlay strategy is
appropriate
• Whethernew materials are required or the existing material can be improved upon
• Whether full reconstruction or partial reconstruction
The consideration ofthe above factors will depend on the analysis of field data collected
during 'Condition Surveys', 'Traffic Surveys' and 'Drainage Surveys.
33
IRC:SP:77-2008
2.5.2. Condition survey data and its analysis: A condition survey of each gravel road
needs to be carried out at least once a year. The condition ofeach road is evaluated as 'Pavement
Condition Index' (PCI) on a rating scale of5 to 1 as detailed below:
-
(a) Based on riding comfort at 40 km/h speed
Smooth - 5
Comfortable - 4
Slightly Uncomfortable - 3
Rough and Bumpy - 2
Dangerous - 1
(b) Based on normal driving speed possible (km/h)
Normal Driving Speed PCI(km/h)
Over 35 5
25-35 4
15-25 3
10-15 2• <10 1
2.5.3. Drainage survey for rehabilitation: The condition survey data will often throw
up indications ofdistresses which are moisture related; e.g. rutting, depressions and potholes etc.
Even if such moisture-related distresses are not evident, there can exist a potential to cause such
distresses. The provisions made for drainage in the original design must be examined in order to
determine their adequacy. The longitudinal and transverse grades, width of pavement layers,
slopes and dimensions of roadside ditches etc. need to be evaluated for their adequacy. Also, a
topographic map of the area must be studied for the surface and subsurface movement ofwater.
The observations on the water level in road side ditches, collection of water on the shoulders,
over the pavement and in the adjoining area are very helpful in evaluating the drainage system.
The properties of subgrade soil, gravel base and gravel surfacing must also be evaluated as part
of the drainage survey. It is only after analyzing the drainage survey data that it is possible to
attribute the types of distresses observed in the condition survey, (as also the potential for such
moisture-related distresses to develop) to deficiencies in the drainage system.
2.5.4. Alternative rehabilitation strategies: After the collection of data fi"om the
Condition and Drainage Surveys, alternative rehabilitation strategies can be worked out
including inter alia. Reconstruction, Regravelling or Routine Maintenance.
More often than not, lack ofproper drainage ofgravel roads is the cause ofdistresses that
get manifested over gravel road surfaces. Therefore, it becomes necessary to augment the
existing drainage system. Simultaneously deficiencies in the properties of sub-base, base and
34
IRC:SP:77-2008
surfacing materials may also exist, as also structural deficiencies in the thicknesses of various
layers to withstand the traffic loads. On the basis of data collected from the Condition Surveys
as well as Drainage Surveys, and considering the comparative costs of the various possible
alternatives, an appropriate rehabilitation strategy should be arrived at.
2.5.5. Selection ofmost appropriate rehabilitation strategy: As per the design criterion
for gravel roads, the performance level should not be allowed to fall below a PCI of 2.0. If,
however, proper maintenance has been neglected, the following guidelines may be followed for
rehabilitation :-
PCI Rehabilitation Measures
1 Reconstruct Immediately
1 to 2 Regravel Immediately;
Routine maintenance to continue
2 to 3 Regravel within 1 year;
Routine maintenance to continue
>3 Routine Maintenance
Overlay thickness requirement of a Gravel Road can be worked out for upgradation/
rehabilitation as per the procedure given in Para 2.3 .4.2
3. CONSTRUCTION AND QUALITY CONTROL
3.1. Choice of Technology
For rural road construction and maintenance, it is advisable to adopt an
intermediate type of technology, somewhere in between the purely manual methods on the
one hand and total mechanization on the other.
Since agricultural tractors are increasingly becoming popular in the rural areas, it would
be both suitable and economical to deploy them for rural road works by suitably
scheduling the operations between agricultural operations and road works. Figs. 3.1 and 3.2
bring out the advantages ofadopting tractor-bound technology.
The appropriate technology recommended for various task operations in rural road
development works is outlined in Table 3.1
.
35
IRC:SP:77-2008
100 -,
MANUALMETHOD
I SEMI-
MECHANISEDMETHOD
EARTH WORK MECHANICAUY STABIUSED LIME STABIUSATION CLAYEY UME STABILISATION CLAYEYSOIL ( 70%.30% ) SOIL (5% LIME) SOIL (3% UME)
Specifications
Fig.3.1 : Unit Cost of Different Specification Using Manual andTractor-bound Tecliniques
30
23
20 .
[||.. |u im || III
00 I I
! ,5
ll l ll l l ll ll ll
10
0 J ii iiiiin iii ni , 11 lllllllllllll,
iiiiiiiiiiiHii , i i iiiiiin iii
EARTHWORK MECHANICALLY STABIUSED SOIL UME STABIUSATION CLAYEY UME STABIUSATION CLAYEY
( 70H:30% ) SOIL (5% UME) SOIL (3% UME)
Fig. 3.2: Percent Saving in Carrying Out Various Operations by Using Tractor-bound
Technology
(Source : Use of Low Cost Agricultural Implements in Low Volume Road Construction
Transportation Research Record, USA)
36
IRC:SP:77-2008
Table 3.1 Choice of Technology For Rural Roads
s.
No.
Item of
Work
Tools/Equipment SuitableRecommendedTechnology for
Rural Roads
Labour
Technology
Intermediate/Semi -
iTXCdlitlllACU
Technology
EquipmentICiliCU
Technology
1. Clearing and
grubbing
Pickaxe,
Hoe, Handshovel, saw,
plough
Rippers towed by
agricultural tractor
Dozers,
Rippers
attached to
Dozers
Labour basedtechnology is
quite efficient,
generates
employment, is
cheap and hencerecommended.
2. Excavation
soil or natural
gravel for
embankment//
sub -base/
base
construction
Hoe, hand
shovel
ivippcia luwcu uy
agricultural tractor
J_/A.LaValUl,
Dozer,
Shovel,
Scraper
Labour bastpcbnnlotJV i<?i>wwixnv^ivy^^ y x.t3
quite efficient,
for the small
volume of work,generates
employment, is
cheap, and hencerecommended.
3. Excavation in
soft rock
Pickaxe,
V_.lUWUcll
Wedging
tools
Dozer,
Excavator
Labour basedtechnology is
quite efficient,
adequate for the
small volumeinvolved,
generates
employment, is
cheap, and hencerecommended.
4. Excavation in
hard rock
Handdrilling and
blasting
Air
compressor,
Jack
hammers,
and blasting
For small jobs,
hand drilling andblasting is
adequate.
For large jobs,
use of equipmentis recommended.
5. Loading and
iinlofldinp of
earth, natural
gravel , stone
materials
Shove!
Hoe
Slhovpl Hop T oaHpr Manual methodsdie di-lwLl U-dlv JLyJl
the small
quantities
involved, becauseof employmentgeneration andrelatively lowcost.
37
IRC:SP:77-2008
Table 3.1 Choice of Technology For Rural Roads
Tools/Equipments SuitableRecommendedTechnology for
Rural Roads
s.
No.
Item of
WorkLabourBased
Technolobgy
Intermidiate
/Semi-
MechanizedTechnology
EquipmentOriented
Technology
6.Hauling of earth,
natural gravel
,
stone materials
l)Lead 0-100 mand wheel
barrow
Labour based technology
is recommended.
2) Lead 100-1000 m Pack animals Animalcart,
agricultural
tractor-
trailer,
trucks
Scraper,
Loader,
Dumper,
Trucks,
Labour based or
immediate technology is
recommended
recommended.
3) Over 1 km —Agricultural
tractor-
trailer,
trucks
Scraper,
Loader,
Dumper
Intermediate technology
is recommended
7. Spreading of soil
or pavement
materials in
layers
Hoe, Rake Blader
attachment
towed by
agricultural
tractor
Grader,
Dozer
Manual method or
intermediate technology
is recommended.
8. Breaking clods
for soil
stabilisation
Wooden Mallet Disc
harrow or
ripper
tnwpH Hv
agricultural
tractor
Disc
harrow or
ripper
towpH bv
dozer or
tractor
Intermediate technology
using agricultural
implements is
recommended.
9. Watering Watering cans Water
Browser
towed by
agricultural
tractor
Self
propelled
Water
Tanker
Intermediate technology
using a water bowser
towed by an agricultural
tractor is recommended.
lU. Mixing stablizer
like lime/cement
and soil
Hoe, rake Disc
harrow and
ripper
towed by
agricultural
tractor
Single pass
Stabliser
Intermediate technology
using agricultural
implements towed by
agricultural tractor is
recommendedbecause of its low cost.
38
IRC:SP:77-2008
s.
No.
Item of
Work
Tools/Equipments Suitable
RecommendedTechnology for
Rural Roads
LabourBased
Technolobgy
Intermidiate/Semi-
MechanizedTechnology
EquipmentOriented
Technology
11. Production of
stone aggregates
1) For Water
Bound MacadamHammer Mobile
crushing
plant with
manual
loading
Crushing
Plant with
screens,
conveyors
and
loaders
Manual breaking of
stones is recommended
for small jobs.
For larger jobs, small
mobile crushing plants
are recommended.
2) For Wet MixMacadam,Concrete and
bituminous
surfacing
Not
recommended
Mobile
crushing
plant with
manual
loading
CrushingPlant
screens,
conveyors
andlofidprs
Intermediate Technology
using mobile crushing
plant and manual loading
is recommended.
12
earthwork sub -
base, WBM and
aggregate base
Rollers pulled
by animals or
human labour
8/10 t
Static
Smooth
Wheel
Roller
Vibratory
Roller8/10 t Static smooth
wheel roller is
recommended.
13. Prime Coat/
Tack Coat
Hand held
cans with
Hand held
lance
JUIU VIUCVJ
with a
sprayer,
operated
by
compressor
Self
propelled
XJllUlllCll
Pressure
Distributor
Intermediate technology
using hand held lance
with a sprayer and
operated by compressor
or hand pump is
recommended
14. Application of
binder for
surface dres sing
11 H Tviiil cir^n1f XZfillUioiiJll
Hand held
cans with
holes
Hand hHH
lance with
sprayer,
operated
by
compressor
Self
propelled
Bitumen
Pressure
Distributor
Hand held lance with
sprayer, operated by
compressor or hand
pump is recommended.
ii) 80/100 Pen.
WlaUC Dl lUinCIl
ndllU ilCiU
cans with
holes
XTctiXCl ilClLX
lance with
sprayer,
operated
bv
compressor
propelled
Bitumen
Pressure
Distributor
Hand held lance with
sprayer, operated by
compressor or hand
pump is recommended.
15. Heating Bitumen Bitumen
Boiler of
Small
capacity
Bitumen
Boiler of
small
capacity
High
capacity
Bitumen
tanks
Bitumen boiler of small
capacity is
recommended.
39
IRC:SP:77-2008
s.
No.
Item of
Work
rip ^ I „ /T7Tools/Ec uipments Suitable
RecommendedTechnology for
Rural Roads
LabourBased
Technolobgy
Intermidiate/Semi-
Mechanizedlecnnoiogy
EquipmentOriented
Tpchnnlnov-1.VvillivlUgY
16. Bitumen Premix
Carpet
Not
recommended
Mini-Hot
Mix Plant
of6t
capacity
Mobile
Hot MixPlant of 20
t capacity
Mini Hot Mix Plant of
6 t capacity is
recommended.
17. Application of
chips for surface
dressing
Manual, by
basket, and
spreading by
rakes
Spreader
box towed
by
agricultural
tractor
Sell
propelled
Chip
spreader
Mannual or intermediate
technology is
recommended.
18. Laying of
Premix Carpet
Manual, by
rakes
Manual by
rakes
Paver
FinisherMannual spreading by
rakes is recommended.
19. Rolling of
i) Chips for
surface dressing
Handoperated
Roller
Not
recommended
8/10 t
static
smooth
wheel
roller
8/10 t
static
smooth
wheel
roller
8/10 t staic smooth
wheel roller is
recommended.
ii) Premix Carpet Not
recommended
20. Production of
Cement Concrete
Hand mixing
Not
recommended
Small
concrete
mixers,
with
weighing
facility
Small
Batching
Plants
Small concrete mixers
with weighing facility
are recommended
21. Vibration of
concrete
Rodding
Not
recommended
1 Needle
vibrators
2 Screeds
for concrete
pavement
3 8/10 t
Roller for
Roller
CompactedConcrete.
1 Needle
vibrators
2 Screeds
3 Vibratory
Roller for
Roller
CompactedConcrete.
1 Needle vibrators for
RCC slabs, beams,
mass concrete.
2 Screeds for concrete
pavement.
3 8/10 t static roller or
vibratory roller for
Roller Compacted
Concrete.
(Source : KadiyaH, Dr. L.R and Lai, Dr. N.B 'Principles and Practices of HighwayEngineering Khanna Publishers, New Delhi, 2006)
40
IRC:SP:77-2008
3.2. Plant Selection and Usage
Table 3.2 gives the plant/equipment considered appropriate and economical for various
field operations in the construction ofgravel roads.
Table 3.2 Appropriate Plant/Equipment for various Field Operations
Construction Operation Appropriate Plant/Equipment
i) Clearing, Grubbing and Excavation.
ii) Hauling of Earth
iii) Spreading of soil/gravel in layers
iv) Adding water to soil
v) Mixing of soil with water
vi) Mixing of different locally available materials
for mechanica I stabilization
vi$ Pulverization of soil clods
vii) Mixing of stabilizer (lime or cement) and water
with soil.
ix) Compaction
Ripper towed by agricultural tractor.
Agricultural tractor-trailor.
Blade attachment towed by agricultural tractor.
Water Bowser towed by agricultural tractor.
Agricultural tractor towed disc harrows.
Agricultural tractor towed Rotavator.
Agricultural tractor-towed disc harrows.
Agricultural tractor-towed Rotavator.
80-100 kN Static smooth-wheeled Road Roller.
3.3. Sequence of Construction Operations : First and foremost in the sequence of
construction operations is the site preparation, as per specified procedure. After site preparation,
the cross drainage works (culverts, causeways etc.) and the surface drains need to be provided as
per the Drainage Plan requirements. The Earth work and Subgrade preparation are then taken up,
(discussed in para 3.4). For a sub-base course, where required to be provided, the materials to be
blended are placed in the required proportions, mixed thoroughly and spread to the desired
thickness and shape, (para 3.5). After compacting the sub-base, the materials to be blended for
the gravel base are placed in the required proportions, mixed thoroughly, spread to the
required loose thickness and shape and compacted to the desired density. The compacted gravel
base is finished to the desired profile (described in para 3.6). Thereafter, a gravel surface course
is laid, compacted and finished to the desired profiles.
3.4. Earthwork and Subgrade Preparation
3.4.1. Earthwork
3.4.1.1. The cost of earthwork generally constitutes 40 to 60% of the total road
construction cost. It is, therefore, essential that careful consideration is given towards site
planning and various operations involved in the execution ofthe earthwork for economizing the
cost of road construction. Since gravel roads are often upgraded later to black-topped flexible
pavement standards as the traffic grows, it is both difficult and uneconomical to make up any
deficiencies in earthwork at a later stage, pointing to the need for strictly adhering to the
specifications laid down in Clause 30 1 ofMORD Specifications. The main activities involved in
earthwork operation are:
(i) Soil survey and laboratory investigations for suitability of material and for
determining theCMC andMDD ofembankment material compaction
(ii) The construction ofembankment.
41
IRC:SP:77-2008
3.4.1.2. Test pits should be dug in borrow areas from where the embankment materials
are to be obtained and representative samples tested for determining their suitability as a fill
material as per the requirements laid down in Clause 301.2.3 of MORX) Specifications.
Ordinarily borrow pits along the road should be discouraged. Where permitted by the Engineer,
the requirements laid down in Clause 30 1 .4. 1 ofMORX) Specifications must be complied with.
3.4.1.3. Prior to the construction operations, the formation for embankment construction
should be prepared as laid down in Clause 301.4 of MORD Specifications. The various
construction operations should be carried out as per Clause 301.5 ofMORD Specifications. The
soil for embankment construction at the time of placement should be at proper moisture i.e.,
(+)2% ofOMC. Additional water should be added ifrequired and the soil should be turned 2 to 3
times so that the water is quite uniformly dispersed. In case the soil contains excess moisture, the
soil should be allowed to dry to bring it the optimum before compaction.
3.4.1.4. For earthwork filling, in layers, the compacted thickness ofthe soil layer should
not exceed 1 50 mm when static smooth wheeled rollers of 80 to 100 kN static weight are used.
When the earthwork has reached a stage when the general form of the final shape of the
embankment has been obtained, the spreading ofthe earth should be done, in straight reaches, to
a crowned shape, and to appropriately superelevated profile if the reach is on a curve. The
moisture content in the laid soil should be the optimum moisture content subjected to the
permitted tolerance. Highly expansive soils such as black cotton soil should be compacted at the
specified moisture content. The clods should be broken to less than 75 mm size. The equipment
for compaction should ordinarily be a 80-100 kN tonne smooth-wheeled power roller. For the
control ofmoisture prior to compaction, a truck mounted water tanker should be used, but in the
absence ofsuch a water tanker, a tractor-towed waterbowser could be used (Fig 3.3).
Fig. 3.3 : A Tractor-towed Water Tanker for Control of Moisture Prior to Compaction
42
IRC:SP:77-2008
3.4.1.5. The tolerance limits of variations from the specified moisture content are
normally ±2% ofOMC. Densities to be aimed at in the compaction process shall be chosen with
due regard to factors such as soil type, height of embankment, drainage conditions, position of
individual layers, and type of available compaction plant, in accordance with Clause 301 of
MORX) Specification. Each compacted layer shall be tested in the field for density, and accepted
before operations for the next layer commence. The field density in the body of the
embankment shall not be less than 97% of standard Proctor density and 100 percent in the top
300 mm of the embankment (Subgrade). Expansive clay (such as black cotton soil) possessing
high volumetric changes should be compacted at a moisture content, wet ofthe optimum and to a
density not exceeding 90 percent of the laboratory standard Proctor density. The overall profile
should be improved with each successive layer so that as the subgrade level is approached, the
profile ofthe formation is as per lines and grades.
The related quality control requirements are detailed in the Quality Assurance
handbook for Rural Roads, 2007.
3.4.2. Subgrade preparation: The top ofembankment which is to receive the hard crust is
called subgrade. The subgrade soil layer shall preferably be made from good soil available
locally. The soil shall be free from vegetative matter and rubbish. In case the reach is at grade or in
cutting and insitu soil is to be used for subgrade, the method consists in loosening the soil to 300
mm depth, bringing the moisture to proper value and compacting it with a suitable roller to
maximum Proctor density. The compaction process should commence at the edges and progress
towards the center. When the reach is in filling, it is necessary to ensure that atleast the top 300
mm of the embankment constituting the subgrade of the pavement should be compacted to 1 00
percent Proctor density in two layers at controlled moisture. The subgrade should be finished to
the desired profile; a camber board should be used to check the cross profile (Fig. 3.4).
The related quality control requirements are detailed in the Quality Assurance
Handbook for Rural Roads.
3.5. Sub-Base Construction
In Gravel Roads, generally a gravel base of required thickness, as per the Design
Catalogue, Fig.2.6 in Section 2, is provided directly over the subgrade, except for the very weak
subgrade (CBR=2), where a capping layer is provided. However, a part of the gravel base
thickness can be converted into a subbase (Fig. 2.7, Section 2) layer having a CBR value in
between the CBR values of the subgrade and the gravel base. The sub-base can be a Granular
Sub-base (GSB) as per Clause 40 1 ofMORD Specifications or Lime-treated soil sub-base, as per
Clause 403 of MORD Specifications or Cement-treated soil sub-base as per Clause 404 of
MORD Specifications, depending on the locally available materials. The salient features of
construction ofthe above three types ofsub-base courses are outlined in paras 3.5.1, 3.5.2 and
3.5.3 below.
3.5.1. Granular sub-base: Where the locally available materials meet the grading,
plasticity and other requirements as laid down in Clause 401 of MORD Specifications, these
43
IRC:SP:77-2008
— LIFTING HANDLE
(a)
LIFTING HANDLE
PAVEMENT SURFACE
DETACHABLE WOODENPROFILE BOARD
Fig. 3.4 : (a) and (b) Two Designs of Camber Board
materials can be used directly without any processing'. However, where the locally available
materials do not meet the various requirements without any processing, the following
mechanical stabilization techniques can be resorted to:
(a) Stabilization of clay with sand, involving the mixing of clay with sand so
that the resulting mixture will have controlled plasticity (PI < 6) and
minimum 30% sand content. The clay shall be excavated and clods broken
by 4 to 6 passes of tractor-towed disc harrows (Fig. 3.5) to meet the specified
pulverization requirements. The soil should be spread in place to the
required loose-thickness. The requisite quantity of sand transported from
local sources is then added. The required quantity of water is added to bring
the moisture content to the optimum. Depth blocks should be used for the
control of required layer thickness (Fi.g 3.6). The mix should then be
compacted by 80 to 1 00 kN smooth-wheeled roller to 100% Proctor density.
44
IRC:SP:77-2008
IRC:SP:77-2008
(b) Stabilization of soil with soft aggregates (such as brick bats, kankar and
laterite) is similar to the mechanical stabilisation of clay with sand as at (a)
above. The soft aggregates to be added to the blended soil mixture shall be
V, of size less than 30 mm and have wet AIV not more than 50%. The blended
soil and aggregate should be mixed together in the ratio 7:3 by volume.
(c) Soil-Gravel/Soil-Moorum mixes shall contain a fair proportion of all
particle sizes together with sufficient clay to provide proper cohesion as per
technical grading limits. The maximum aggregate size should not exceed
one-third the thickness of stabilized layer. The construction shall otherwise
be carried out in the same manner as for other mechanically stabilized soil
construction. Care should be taken that the layer is thoroughly compacted
and laid to proper profile.
3.5.2. Lime stabilized soil construction
The specification for lime stabilized soil construction shall apply essentially to
stabilization of alluvial soil, moorums, clays and black cotton soils. As mentioned earlier, the
borrow areas may be previously watered for easy excavation. The excavated soil shall be
pulverized, so that all soil clods pass the ISS 26.5 mm sieve and more than 80% through ISS 4.75
mm sieve using tractor-towed disc harrows. In case ofblack cotton soil, the borrow areas shall be
previously watered and the clods which are generally in the size range of 1 00- 1 50 mm should be
pulverized with agricultural equipment (disc-harrows), and Rotavator (Fig. 3.7). The pulverized
soil (alluvial/moorum/ black cotton soil) shall be spread on the prepared receiving surface, and
slaked lime spread over it in the required quantity (Fig. 3.8) as per the guidelines provided in
Clause 403 ofMORD Specifications. For the safety ofworkers, hand gloves should be provided
while handling lime. The laid material shall be cut and mixed thoroughly, using a
tractor-towed Rotavator. The mass shall then be spread to the required loose
thickness to proper profile. The compacted thickness of a layer shall not exceed 1 50 mm if 80-
1 00 kN smooth wheeled roller is used. The laying width shall extend by 150 mm on either side,
beyond the pavement width on top. The layer shall then be thoroughly compacted without much
delay (within 3 hours) after mixing with lime with a 80- 1 00 kN smooth-wheeled roller giving 6-8
coverages as for earthwork. The subbase layer shall be checked for compaction. All controls and
permitted tolerances shall be as given in Clause 403 ofMORD Specifications. The surface after
compaction shall be cured for 7 days by sprinkling water periodically, covering by wet gunny
bags (Fig. 3.9) soon after which subsequent pavement courses shall be laid to prevent the surface
from drying out and becoming friable. The traffic shall not ply directly over the stabilized layer
during the period of curing. The related quality control requirements are detailed in the Quality
Assurance Handbook for Rural Roads.
3.5.3. Cement stabilized soil construction
For cement stabilized soil construction, the various construction operations and the
equipment deployed are essentially the same as for lime stabilized soil construction except that
compaction should be completed within 2 hours after mixing.
46
IRC:SP:77-2008
IRC:SP:77-2008
Fig. 3.9 : Curing by Covering the Compacted Stablized Soil Surface with
Wet Gunny Bags
3.6. Gravel Base/Surface Course Construction and Quality Control
While detailed specifications are contained in clause 402 ofMORD Specifications, the
salient features ofthe Methodology to be adopted and the Quality Control requirements are given
below:
A. METHODOLOGY
1. The Gravel/Soil-Aggregate in base and surface course shall meet all the
physical requirements set forth in Para B and conform to the gradings given in Table
2.1 of Section 2 for base course and in Table 2.2 ofSection 2 for surface course.
2. Before receiving the Gravel/Soil-Aggregate material, the subbase/base, as the case
may be, shall be prepared to the specified lines and crossfall. Any existing ruts,
predominant irregularities or soft yielding places should be corrected and rolled
until a firm surface is obtained.
3 . The Gravel/Soil-Aggregate material meeting all the specified requirements shall be
spread on the prepared surface with the help of a grader of adequate capacity, for
maintaining the required slope and grade.
4. Where com.bination of different materials is required for obtaining the
Gravel/Soil-Aggregate meeting the specified requirements, mixing shall be done
mechanically by the mix-in-place method.
5. The equipment for mix-in-place shall be a tractor-towed rotavator or similar
equipment capable ofmixing the materials to the desired degree.
48
IRC:SP:77-2008
6. It must be ensured that prior to compaction, the moisture content is within 2 percent
of the optimum moisture content, making due allowance for evaporation losses.
After adding the required quantity of water, the material should be processed bymechanical means like tractor-towed disc harrows/rotavators until the layer is
uniformly wet.
7. Rolling shall be carried out as per Para 402.4.2 ofMORD Specifications.
8. The density to be achieved should be 100% of the maximum dry density for the
material determined as per IS:2720 (Part 7).
9. Any loose, segregated or otherwise defective areas should be made good to full
thickness oflayer and re-compacted.
B. QUALITYCONTROLREQUIREMENTS
1 . Materials
(i) The grading for Gravel/Soil-Aggregate Base shall conform to the requirements
given in Table 2.1 of Section 2 while the grading for Gravel/Soil-Aggregate
Surface Course shall conform to the requirements given in Table 2.2 of Section 2.
(ii) Wet Aggregate Impact Value (IS:5640) shall not exceed 40 and 30 when used in
base and surfacing respectively.
(iii) The needed gradation shall be obtained by crushing, screening and blending
processes as necessary.
(iv) Fine aggregate material passing 4.75 mm sieve shall consist ofnatural or crushed
sand and fine mineral particles.
2. HorizontalAlignment
The edges of the Base shall be correct within a tolerance limit of (+) 30
mm in plain and rolling terrain and (±) 50 mm for hilly areas. The edges of the
carrigaeway with Gravel/Soil-Aggregate Surfacing shall be correct within (±) 20
mm in plain and rolling terrain and (±) 30mm in hilly terrain.
3. Surface Levels
The tolerance in surface level for Gravel/Soil-Aggregate Base and
Surface will be restricted to (±) 10 mm. A grid of 10 m by 2.5 m may be
formed to check the surface level.
4. Surface Regularity
The maximum permitted difference between the Gravel/Soil-Aggregate
layer and 3 m straight edge shall be 1 2 mm for longitudinal profile and 1 0 mm for
cross profile. The cross profile should conform to the prescribed camber.
5. Degree ofCompaction
Density shall be 100 per cent ofmaximum dry density for the material determined
asperIS:2720(Part7).
49
TRC:SP:77-2008
6. Quality Control Tests
The quality control tests and their frequency for gravel/soil-aggregate base and
surface construction shall be as per Tables 3.3, 3.4 and 3.5, as laid down in the
QualityAssurance Handbook for Rural Roads.
Table 3.3 : Quality Control Tests Prior to Construction
Type of Test Frequency
1. Soil Classification as per IS: 1498.
1 . Wet Sieve Analysis, except for cohesionless soil.
2. Liquid Limit and Plastic Limit
One test from each source identified
by the Contractor.
2. Combined Grading and Plasticity tests on materials
from different sources, mixed in the design proportions.
This shall be done when materials from more than one
source are combined.
One test on the combined material.
3. Proctor compaction Test (IS:2729 Part 7) One test on the material from each
source or on the combined material,
as the case may be.
4. Wet Aggregate Impact Value Test (IS: 5640) where
soft/marginal aggregates are used e.g., Laterlite,
Kankar etc.
One test from each source identified
by the contractor.
5. CBR test (IS:2720 Part 16) on representative sample
compacted at 100% Proctor dry density.
One test per km length.
Note : Where materialsfrom more than one source are to be combined in the desired
proportions, the tests at SI. Nos. 2, 3 and 5 should be carried out on the combined
material.
Table 3.4 : Quality Control Tests During Construction
Type of Test Frequency
1. Wet Sieve Analysis (18:2720 Part 4) on the
GSB material combined in the design
proportions from various sources
Atleast one test to be carried out
daily.
2. Liquid Limit and Plastic Limit tests (IS:2720
Part 5)
-do-
3. Placement Moisture Content (IS:2720 Part
2)
Atleast 3 tests to be carried out
daily, well spread over the day's
work.
4. Insitu Density measurements (18:2720 Part
28)
-do-
50
IRC:SP:77-2008
Table 3.5 : Quality Checks by AE/EE
Stage Test Frequency
Designation
of
Inspecting
Officer
1 . Top of the First
Layer before
placing the next
Gravel layer
i) Degree of
Compaction
(IS:2720 Part 28)
i) Minimum 3 tests for each
km length or part thereof;
ii) Individual test values of the
degree of compaction
attained shall not be less
than 1% of the specified
degree of compaction. For
example, for the required
degree of compaction of
100% Proctor Density, the
individual test values shall
not be less than 99% of
Proctor Density and the
average of three (or more)
tests carried out in a day
allali IlUl UC less llldll iUU/0
Proctor Density).
AE
AE
ii) Surface
Regularity and
Transverse Profile
Random Checking AE
Z,. iT llllSllCU. VJlctVCl
Layer
ij L-'CglCC Ui
compaction
(IS:2720 Part 28)
Ij WllC LC^l iUl CctCll Z,JU ill
length or part thereof
length or part thereof
AF
FF
ii) Surface
Regularity and
Transverse Profile
Random Checking AE
51
IRC:SP:77-2008
C. DO'S AND DON'TS
1.
Do's
While preparing the subbase/ base, where
predominant irregularities exist, make sure that
the surface profile is corrected before spreading
the Gravel/ Soil-Aggregate Mix.
For the equipment used for mix-in-place
construction, carry out trial runs to establish the
suitability for the work.
Look for soft patches, ifany and rectify them by
removing or adding fresh material and
compacting the same throughly.
For obtaining the needed uniformly ofmixing of
water with Gravel/Soil-Aggregate, sufficient
passes of mechanical equipment like tractor-
towed disc harrows/ rotavators should be
ensured.
Adopt Tractor-Bound Technology, using the
local agricultural tractors.
Make sure that the earth used in the earthen
shoulders has the requisite properties and is
compacted to 100% Proctor Density and that
proper cross slopes ( 1% steeper than camber)
are provided.
3.
5.
Don'ts
Do not permit any organic or
deleterious material.
Do not allow manual mixing,
unless the width of laying is not
adequate for mechanical operations,
as in small-sizedjobs.
Do not allow the speed of the roller
to exceed 5 km per hour.
Do not allow sharp turns with the
compaction equipment because
they can cause surface roughness.
Do not leave the side slopes
un-turfed, otherwise rain cuts
would be formed.
Do not forget to provide a well-
designed drainage system, with
properly identified outlets.
3.7. Providing Gravel Surface
Over the finished base course, a gravel surfacing material meeting the specified
requirements given in Chapter 2 is spread to the required loose thickness, compacted to the
required density and finished to the desired profile.
It is good practice to place a thin layer of about 12 mm size broken stone or gravel. This
layer is intended to act as a "Cushion" between the wheel load and the base course. It is supposed
to absorb some ofthe abrasive forces ofa passing wheel. The use ofthis thin layer is optional, but
in many cases it has been noted that ifa running course is not separately provided, it will develop
naturally on its own. In light grading, the motor grader or drag works on the running course and
thus does not cut into the base course with its water resistant crust. If maintained evenly spread
over the carriageway, then the rest ofthe pavement should last a long time and should not dry out
very quickly in dry weather.
In general, running course is a protection against erosion caused either by climate or
vehicle loadings.
52
IRC:SP:77-2008
3.8. Sealing a Gravel Road
3.8.1. Before applying bituminous surface treatment, any existing surface gravel with a
PI exceeding 10 shall be scarified and removed and the existing surface brought to proper
transverse profile. Any irregularities in the longitudinal and transverse direction must be
removed. If any granular layer overlay is required, the same should be implemented. Prior to
applying the bituminous treatment, the prepared gravel surface must be primed by spraying a
Slow Setting Bituminous Emulsion with a kinematic viscosity of250-500 Centistokes at 60''C at
the rate of 1 2- 1 5 kg per 1 0 sqm area. Surface Dressing is considered a preferred surface treatment
for low volume rural roads. The selection of the size of stone chippings should be based on the
anticipated traffic and the type of surface to be provided with the bituminous surface treatment.
The design of surface dressing may be done in accordance with the design procedure
recommended in IRC: 11 0-2005 Standards specifications and Code of Practice for Design and
Construction ofSurface Dressing.
3.9. One-Coat and Two-Coat Surface Dressing
3.9.1. Whether one-coat or two-coat surface dressing is to be provided on a rural
road shall be decided on the basis of anticipated traffic and climatic conditions.
3.9.2. The cover material shall consist ofcrushed stone, crushed gravel (shingle) or other
stones. It should be clean, strong, durable and of fairly cubical fragments, free from disintegrated
particles, vegetable matter, dust and adherent coatings.
3.9.3. The surface dressing work shall preferably be carried out when the atmospheric
temperature in shade is lO^C or above. The bituminous material shall not normally be applied
when the surface or the cover material is damp, weather is rainy or during dust-storm. The
underlying course on which surface dressing is to be laid shall be prepared, shaped and
conditioned to a uniform grade. The surface should be swept clean free of caked earth and other
foreign matter with hard brushes, then with softer brushes and finally blown off with sacks or
gunny bags to remove fine dust. When the base to be treated is gravel or stabilized soil, a
bituminous primer coat shall be applied uniformly at the specified rate. After priming the base,
the bituminous binder shall be spread at the rate determined as per IRC: 11 0-2005. Immediately
after the application of bituminous material (Fig. 3.10) the cover material shall be spread in
required quantities by suitable means so as to cover the surface completely. The surface shall be
broomed to ensure uniform spreading.
3.9.4. The entire surface shall then be rolled immediately after the application of cover
material with a suitable roller. The rolling shall begin at the edges and proceed towards center,
except on the super-elevated portions, where the rolling should proceed from the inner to the
outer edge. Additional aggregates shall be spread in whatever quantities may be required to fill
irregularities and to prevent picking up ofthe aggregate by the roller.
3.9.5. The finished surface shall be opened to traffic on the following day. Ifunder some
special circumstances, the road has to be opened to traffic immediately after rolling, speed of
traffic shall be limited to 1 6 km per hour until the following day.
3.9.6. The quahty of materials, construction etc. for two coat surface dressing shall be
similar to one coat surface dressing. Prior to the application of second coat, the surface shall be
cleaned properly. Binder, heated to appropriate temperature, shall be sprayed, preferably with a
mechanical sprayer, at the specified rate.
3.9.7. Immediately after the application of binder, the cover material shall be spread
by suitable means at the specified rate to cover the surface completely. The rest of the process
53
IRC:SP:77-2008
of rolling, finishing and opening to traffic shall be similar to one coat surface dressing.
(a) Spraying Bituminous Material over Prepared Surface
(b) Spraying Cover Material
Fig. 3.10
3.10. Step-wise Procedure for One-Coat and Two-Coat Surface Dressing
(a) The material viz. aggregates and binder should be checked for specification
requirements.
(b) All depressions and pot holes etc. on the receiving surface should be corrected.
(c) The receiving surface should be cleaned by brushing to ensure that there is no
loose material before binder is applied.
(d) If bituminous primer coat is applied, it should be cured before laying surface
dressing.
(e) No surfacing work shall be carried out if-
(i) atmospheric temperature in shade is less than 1 0°C or
(ii) base is damp or
(iii) construction materials are damp or
(iv) the weather is foggy, rainy or dusty;
(f) The work should be so organized that no traffic or dust gets on to the cleaned or
bitumen painted base.
(g) The rate of spray of binder should be regularly checked using tray method. Theends of the stretch should be covered with thick paper so as to avoid double
spraying of binder. The temperature of binder at the time of application should
also be checked.
(h) Immediately after application of binder, the aggregates should be uniformly
spread; ifneeded, use brooms for spreading.
(i) The rolling on aggregates with approved roller shall commence immediately
54
IRC:SP:77-2008
from the edges progressing gradually towards the center parallel to the center
line. At super-elevation, it should proceed from inner edge to outer edge,
(j) Rolling operations should be continued till aggregates are firmly embedded in
binder.
(k) Second coat, ifspecified, can be laid after 2 to 3 weeks.
(1) Finished surface should be checked for cross and longitudinal profiles using 3 mstraight edge.
(m) No traffic should be allowed for 24 hours. If cutback/emulsified bitumen is
used, the finished surface should be closed to traffic till the binder is adequately
cured/set.
3.11. Step-wise Procedure For Providing 20mm Bituminous Premix Carpet
(a) The materials viz., aggregates and bituminous binder should be checked for
specification requirements.
(b) The underlying surface on which the bituminous surfacing is to be laid should
be suitably prepared, with all depressions and potholes etc. corrected, shaped
and conditioned to the specified lines, grades and cross-sections.
(c) The receiving surface should be cleaned by brushing to ensure that there is no loose
material on the surface.
(d) A prime coat where needed should be applied as per specified procedure, using
hand held lance provided with a sprayer, operated by compressor. Use of hand
held cans with holes should not be permitted.
(e) Tack coat should be applied at the specified rate uniformly on the prepared
base, using hand held lance provided with a sprayer, operated by compressor.
(f) Mixing of aggregates and bitumen in specified quantities should be carried out
in a Mini Hot Mix Plant of preferably around 6 t/hour capacity, carefully
controlling the specified temperature of heated aggregates and bitumen and the
mixing temperature.
(g) The hot mix should be immediately transported from the mixer to the point of
use in suitable vehicles or hand barrows. The vehicles should be clean and the
mix being transported should be covered in transit.
(h) The pre-mixed material should be spread even to specified thickness and
camber, making due allowance for any extra quantity required to fill up
depressions. The cross-fall should be checked by camber boards and any
irregularities leveled out.
(i) Rolling should begin at the edges and progress towards the center
longitudinally, except that on superelevated and uni-directional cambered
portions, it should progress from the lower to upper edge parallel to the center-
line. Wheels ofthe roller should be kept moist.
(j) Rolling should be continued until the entire surface has been rolled and all
roller marks eliminated,
(k) A seal coat where specified should be applied to the surface immediately after
laying the surfacing.
(1) The finished surface should be checked for line, level and regularity using
camber board/straight edge
.
(m) Traffic may be allowed on the surface once it has reached ambient temperature,
but speed must be rigorously restricted to not more than 1 6 km per hour.
55
IRC:SP:77-2008
4. MAINTENANCE METHODS AND MANAGEMENT SYSTEM
4.1. General
4. 1.1.While proper maintenance of all types ofroad pavements is important, it is a matter
of crucial importance for the satisfactory performance of Gravel Roads. Even though Gravel
Roads require more frequent maintenance interventions than black-topped roads, these
interventions are relatively inexpensive and simple, within the available resources and skills in
rural areas. Specially designed studies as well as experiences all over the World show that for low
volumes of traffic upto about 200 vehicles per day, the maintenance costs of gravel roads work
out to be lower than for black-topped roads, while for higher volumes oftraffic, it is the other wayround. It is mainly the neglect of proper maintenance that is responsible for gravel roads not
gaining popularity in the vast rural areas of India with low to very low volumes of traffic. With
simple inexpensive maintenance interventions, gravel roads can be easily maintained in good
condition. The simple and labour intensive maintenance methods also hold considerable
potential for employment generation.
4.1.2. Causes of deterioration : A gravel road deteriorates in its level of service ability
with age, basically due to following factors:
(a) Traffic: The traffic operating on the facility can cause different types ofdistress like
rutting, corrugations, loss of materials, and structural deformation. The extent of
deterioration depends upon the intensity of traffic, especially the wheel load and its
repetitions. Solid-wheeled cart traffic can be very damaging to the road, since the
solid wheels cut into the pavement causing deep ruts.
(b) Environment: The external influence of environmental factors such as rainfall and
snowfall, can also cause deterioration of the pavement. Rainfall causes erosion of
shoulders and slopes and ingress ofwater into the pavement structure and subgrade
and affects the performance of drainage structures. Snowfall can cause ingress of
moisture into the pavement structure and subgrade and result in frost action. The
influence of the environment on a gravel road is much more severe than on black-
topped/ concrete roads.
4.1.3. Maintenance operations
(a) The various maintenance operations on gravel roads can be broadly classified into
the following categories :-
(i) Routine maintenance, comprising patch repairs; dragging, grading,
maintenance of shoulders and repairs to roadside drains, road signs, culverts
etc., and collection of data such as road condition and traffic surveys, which
are required to be carried out by the maintenance staff once or twice every
year.
(ii) Periodic maintenance, which consists ofwork items such as 'Regravelling' to
be carried out periodically every few years.
(iii) Special repairs, and flood and rain damage repairs, which consist of repairs
to the embankment, pavement, culverts, road furniture, etc. necessitated by
56
IRC:SP:77-2008
landslides, earthquakes, cyclones, heavy rains/cloud bursts, floods etc; the
nature and extent of such repair works could not be foreseen or predicted.
(b) Before starting with the work, it should be ensured that adequate
arrangements (like erection of barriers, signs and red flags/light/reflectors) (Fig.
4.1) are made for the safety of traffic, workmen, pedestrians, cattle etc. The work
should be planned in such a way that inconvenience caused to the traffic is minimal.
Wherever possible, the work should be confined to half the pavement width at a
time, leaving the other halfto traffic.
4.1.4. Economic benefits ofmaintenance operations
Timely and proper maintenance of Gravel Roads can lead to significant economic
benefits. These include:
(i) Reduction in level of future maintenance and rehabilitation costs.
(ii) Improved safety and reduction in road closures.
(iii) Reduction in vehicle operating costs and accident costs.
4.2. Surface & Structural Defects on Gravel Roads
4.2.1. The defects observed on Gravel Roads are essentially the result of complex
interactions between the materials used, traffic type and volume, climatic conditions,
construction methods and quality control exercised. Broadly, the various defects can be
classified as:-
(a) Surface defects, observed in the upper layers of the pavement are due to
factors like poor compaction, unsatisfactory grading, climatic conditions,
poor quality of materials, inadequate drainage, neglect of routine and
preventive maintenance measures etc. or a combination of these. The surface
defects result in poor riding quality. The more common surface defects are:
- Corrugations
- Potholes
- Rutting
- Ravelling/Loose Material
- Surface Erosion/Dust Generation/Loss ofSurface Material
- Slippery Surface
- Soft Spots
(b) Structural Defects, are deep seated problems caused by overstressing of the
subgrade and/or the pavement. One ofthe common causes is lack ofdrainage, other
causes being substandard materials used and inadequate thickness of the pavement
for the design traffic. These defects are often characterized by shear failure in form
oflarge settlements and upheavals.
57
IRC:SP:77-2008
MEN WORKING AHEADSIGNS
END OF WORKSITE SIGNS STOP/GO PADDLE
FOR TFIAFFICCONTROLLER
WORKER'S FLUORESCENT JACKET
TRUCK WITH REFLECTIVE MARKINGS
Fig. 4.1 : Some Safety Devices for the Workmen(Source:Intemational Road Maintenance Hand Book Vol. II, Maintenance
of Unpaved Roads, PIARC, Published by TRRL, UK)
58
IRC:SP:77-2008
4.2.2. Surface defects can be removed by grading or planing the surface. However, gravel
roads with structural defects would require a more detailed investigation and treatment including
rehabilitation.
4.2.3. During the Condition Survey of any Gravel Road, it is necessary to make an
assessment of the severity of surface defects in terms of the severity being 'High', 'Mediun' or
'Low'. Such an assessment can be accomplished as under:
(a) Surface Roughness/Riding Quality (Refer para 2.5.2 Section 2)
An assessment shall be made in terms ofthe 'Pavement Condition Index' (PCI) on a rating
scale of5 to 1 as under:
Normal Safe Driving Speed (km/h)
Over 35
25-35
15-25
10-15
Less than 10
(b) Corrugations
PCI
5
4
3
2
1
A visual assessment of the corrugations shall be made by the bumps experienced while
travelling on the gravel road in ajeep or passenger car as under:
(i) Bumps can be felt and heard and significant
reduction in speed is required
(ii) Bumps can be felt and heard and some
reduction in speed is required
(iii) Bumps can be felt and heard but no
reduction in speed is required
High severity
Medium severity
Low severity
(c) Potholes
A visual assessment ofthe severity of'Potholing' shall be carried out as under:
(i) Depth ofpothole more than 50mm High severity
(ii) Depth ofpothole in the range 25 to 50mm Medium severity
(iii) Depth ofpothole less than 25 mm Low severity
(d) Rutting
The ruts or depressions ofthe surface in the wheel tracks shall be measured in mm and an
assessment ofthe severity level made as under:
(i) Depth ofrutting more than 50mm(ii) Depth ofrutting 25 to 50mm(iii) Depth ofrutting less than 25 mm
High severity
Medium severity
Low severity
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IRC:SP:77-2008
(e) Ravelling
An assessment of the percentage area of the ravelled surface shall be made and
severity level recorded as under:
(i) Percentage area ofravelled surface over 50 High severity
(ii) Percentage area ofravelled surface 25 to 50 Medium severity
(iii) Percentage area ofravelled surface < 25 Low severity
(f) Surface Erosion
Gravel roads are susceptible to longitudinal/transverse erosion by flow ofwater over the
road surface. An assessment of the severity level can be made by the bumpiness experienced
while driving in a car orjeep over the eroded surface, as under:
(i) Bumps can be felt and heard and significant
reduction in speed is required High severity
(ii) Bumps can be felt and heard and some
reduction in speed is required Medium severity
(iii) Bumps can be felt and heard but no
reduction in speed is required Low severity
(g) Dust Generation
An assessment of the dust nuisance shall be made by driving in a car/jeep at a speed
of 30-40 km/h and taking observations as under:
Dangerous loss of visibility - significant discomfort High severity
Some loss of visibility - no discomfort Medium severity
No loss of visibility Low severity
4.3. Maintenance of Gravel Roads
The maintenance methods commonly adopted for Gravel Roads are Grading, Dragging
Patching, RegraveUing and use ofDust Palliatives, described in sub-paras 4. 3.1 to 4.3.5.
4.3.1. Grading
4.3.1.1. It is a matter of vital importance that a good camber is always maintained on a
gravel road surface to enable the water to shed off readily. Such a maintenance effort can be
accomplished by regular 'Grading'. For Gravel Roads, the 'Grading' is also needed to restore
gravel from the shoulders which has been lost from the Gravel Road surface and the gravel thus
restored can be used to fill potholes and corrugations etc. Grading can be used to correct the
following defects:
- Loss of Shape
- Ruts
- Potholes
- Corrugations
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IRC:SP:77-2008
- Erosion Gullies
- Silted or Blocked Ditches
4.3.1.2. Grading is a 'Routine Maintenance' activity and can be carried out by tractor-
towed graders. The gravel road surface to be graded should first be prepared by patching of large
potholes or depressions and draining out areas of standing water etc. It may be necessary to
scarify the existing surface to cut to the bottom ofany surface defects and loosen the material for
reshaping. The process ofgrading can be carried out by tractor-towed grader (Fig. 4. 2). Grading
can be ofthree types, as under:
• Light Grading : When the gravel surface crust is not broken and it is a matter of
only spreading or raking back loose surface material to provide a "running course"
as protection ofthe surface crust.A light Grader or Drag can serve the purpose.
• Normal Grading : This is done when the surface crust is cut and it is necessary to
remove surface defects such as corrugations, ruts or potholes. In this case a 8-10
tonne Grader is suitable.
• Heavy Grading : This is required when the road is out of shape and in the process
of repair, and fairly heavy scarifying is required. This reshaping operation requires
a Grader in the 10-12 tonne mass range.
4.3.1.3. The Grader works on one side ofthe road at a time and works in passes about 200
metres long to convenient and safe turning points (Ref. 1 ). Light Grading will normally require 4
passes to reshape the road (Fig. 4.3). Heavy Grading will require additional passes to achieve the
required camber. Work should be completed on one side ofthe road at a time. An even number of
passes should be used to avoid a flat finished crown. The initial passes cut to the bottom of the
surface irregularity and deposit a windrow just beyond the centre line. If required, water should
be sprayed over the windrow. In order to avoid flattening the centre, the final pass should not be
made down the centre ofthe road with the grader blade horizontal (Fig. 4.4).
4.3.1.4. On sections where grading has been completed, the road roller should follow.
Normally about 8 passes of the roller are required to achieve full compaction, working towards
the centre. Shoulders should be treated as part ofthe running surface. Camber should be checked
with a Camber Board at about 1 00m intervals. On bends, the surface should be straight at 4 to 6 %from shoulder to shoulder. The shape ofthe road over the culverts should be maintained to avoid a
hump (Fig. 4.5). Where required, material should be brought from either side of the culvert to
maintain the required cover to the top ofthe culvert.
4.3.1.5. The number of times during the year each Gravel Road will need grading will
depend upon the amount of traffic using the road, climatic conditions in the area, local
topography and other physical features. In the absence of adequate experience in the area, the
Grading Frequency Chart developed by theTRRL ofUK (Fig. 4.6) may be used.
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IRC:SP:77-2008
LIGHT GRADiNG
200 m approx
HEAVY GRADING
Fig. 4.3 : Light and Heavy Grading
ource: International Road Maintenance Hand Book Vol. II,
Maintenance of Unpaved Roads, PIARC, Published
by the TRRL, UK)
63
IRC:SP:77-2008
Fig. 4.4 : Avoid Flattening at tlie Centre (Ref 1)
(Source : International Road Maintenance Hand Book Vol. 11,
Maintenance ofUnpaved Roads, PIARC, Published by the TRRL, UK)
Fig. 4.5 : Avoid Hump at Culvert
(Source : International Road Maintenance Hand Book Vol. II, Maintenance of UnpavedRoads, PIARC, Published by the TRRL, UK)
8
50 100 150 200 250 300
Annual average daily traffic (vehicles per day)
Fig. 4.6: Grading Frequency Chart
64
IRC:SP:77-2008
4.3.2. Dragging
4.3.2.1. Dragging is normally a Routine Maintenance task used to improve the gravel
road surface. Regular Dragging smoothens out minor defects in the road surface and removes
loose material from the surface. Where a running course of sand/gravel is used to cover the base
material for protection from traffic wear, frequent dragging is used to redistribute the running
course material disturbed by traffic plying over the surface.
4.3.2.2. Specially made drags towed by agricultural tractors can be used for Dragging.
Where the traffic plying on a rural road is of a low order, frequent dragging can reduce the need
for Grading. It is generally after a number of dragging operations that Grading is required.
Dragging will not remove corrugations once they are formed, nor will it restore camber or lost
material.
4.3.2.3. Dragging may be considered suitable only when development of road has been
carried out to a level when the pavement is structurally sound and where the loose running course
is less than 25 to 30mm in depth.
4.3.2.4. For various road conditions, the recommended plants are given below:
Road Condition Recommended Plant
Roads with depths of loose material in
excess of 20 mmBroom drag
Cutting drag using old grader blades.
Towed grader or light power grader.
Roads with roughness levels* less than
6000 mm/km with no appreciable loose
material
Timber framed drag or broom drag
Light grader or planer
Roads with roughness levels greater than
6000 mm/kmCutting drag using old grader blades.
Light grader, planer or mediumgrader
* Roughness measured using Bump Integrator
Drags should not be towed at speeds above 1 0 km/h and preferably should be towed at 5km/h. Abroom drag and roller can be seen in Fig. 4.7, while a typical tractor and timber drag are shown in
Fig. 4.8. In Fig. 4.9, it can be seen how a drag can be used to shift material from different parts of
the pavement.
4.3.2.5. It must be emphasised that Drags must be used at frequent enough intervals to
smoothen the road surface. Drags should not be used on roads which have deteriorated, due to
lack of frequent maintenance interventions, to a level where only heavy grading or reshaping is
the answer. Fig. 4.10 shows a multi-purpose tractor-towed equipment enabling an operator to
carry out a wide range ofmaintenance activities.
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IRC:SP:77-2008
Fig. 4.7 : A Broom Drag(Source:Unsealed Roads : A Manual of Repair and Maintenance
for Pavements, National Roads Board, New Zealand)
Fig 4.8 : Typical Tractor Towed Drag
(Source:Unsealed Roads : A Manual of Repair and Maintenance for
Pavements, National Roads Board, New Zealand)
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IRC:SP:77-2008
DRAG IN USE AS SEEN FROM ABOVE
DIRECTION OFTRAVEL
MATERIALBEING DRAWNFROM CENTREOF ROAD TO
SIDES
DIRECTION OFTRAVEL
MATERIALBEING DRAWNFROM SIDESTO CENTREOF ROAD
DIRECTION OF jT*>TRAVEL
MATERIALBEING
SMOOTHENED
Fig. 4.9 : Use of Drag in Drawing Material from Different Parts of Pavements
(SourceiUnsealed Roads : A Manual for Repair and Maintenance for
Pavements, National Roads Board, New Zealand)
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IRC:SP:77-200
!
Fig. 4.10 : A Tractor-Towed Equipment Enabling the Operator to Carry out a
Variety of Maintenance Operations
(Source:Unsealed Roads : A Manual of Repair and Maintenance for
Pavements, National Roads Board, New Zealand)
4.3.3. Patching
4.3.3.1. Where potholes or depressions on the gravel road are large, patching is required
before grading. Sometimes, patching is required between grading or reshaping operations.
Patching can be used to repair eroded areas or can be used to restore areas which become soft
when wet. When the work involves material less than a truck or two, the repair work is termed
patching, while for large scale work, it is termed Spot Gravelling or Regravelling. Patching
cannot be used for repairing Corrugations but can be used to correct:
- Erosion Gullies
Where the potholes are large in numbers, scarifying will be needed with a grader and
possibly Regravelling.
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IRC:SP:77-2008
4.3.3.2. Gravel to be used for patching should be dumped by the road side where it is
required to be used. The quaHty of gravel should be at least as good as the gravel already used in
the road surfacing. The gravel should be dumped on the shoulder (Fig. 4.11) adjacent to the
location where the patching work is to be carried out. Care must be taken to see that the material
should not be dumped on the road surface.
4.3.3.3. In the pothole or rut, where patching work is to be carried out, any loose material
or standing water should be brushed out (Fig. 4.11). Where the potholes are large in size or are
very deep, the sides should be cut back to be vertical.
-V" (a) ' (b)
Fig. 4.11 :(a) Dump the material on the shoulder adjacent to location of patching work(b) Brush out any loose material or standing water
(Source: International Road Maintenance Hand Book Vol. II, Maintenance of UnpavedRoads, PIARC, Published by the TRRL, UK)
4.3.3.4. Check the moisture content of the material. If it is dry, the area to be patched
should be sprinkled with water and also water should be added to the material to be used for
patching. The area should be filled with gravel to a depth ofabout 100 mm. Ifthe material is dry,
it should be sprinkled with water to assist compaction.
4.3.3.5. The 1 00 mm layer at a water content close to OMC, should be compacted using a
roller or a hand rammer. In this manner, patching is built up in layers. The patched area is thus
filled up with gravel to about 30 mm proud of the surface level and is spread and raked to the
correct shape. The patch is compacted by a roller if the area is large and by hand rammer if the
area is small. Even for large areas, hand rammers will be required for the short edges and comers.
4.3.4. Regravelling
4.3.4.1. Regravelling is a periodic maintenance operation. Well before any significant
reduction in base thickness takes place and before the PCI rating reduces to the terminal PCI of
2.0, the task of 'Regravelling' must be accomplished. Regravelling can be carried out to correct
the following defects :-
- Loss ofshape
Ruts
- Potholes
- Erosion Gullies
Grading or Reshaping should be carried out before the regravelling operation.
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IRC:SP:77-2008
4.3.4.2. Gravel obtained from a quarry or gravel pit must meet the specified quality
requirements and the needed approval obtained before commencement ofthe work. The sections
where Regravelling is required should be marked at the site. The existing road surface must be
graded to provide a firm regular surface and the edges should be boxed to provide lateral support
for the fresh gravel. The graded surface should be watered to have the water content close to
OMC and roller compacted. The camber should be checked with a Camber Board and it should
fall within the specified range.
4.3.4.3. The Drainage System should be checked and repaired where necessary. The
excavated gravel should be stockpiled in low heaps to prevent segregation. After the initial
grading of the road is complete, the gravel should be transported to the regravelling site. The
dumping ofgravel should start at the far end ofthe site so that the gravel heaps do not come in the
way oftrucks delivering later loads.
Materials should be dumped at correct spacing on one side ofthe road only.
AWeekly Gravelling Plan should be prepared to indicate hauling distance etc.
4.3.4.4. Spreading ofthe gravel can start when there is a working length of at least 200 mof dumped material. Initially the road is sprayed with water. The Regravelling material is then
spread across the road using the grader. The material is then alternately spread by the grader and
watered until its moisture content is close to OMC. The material is then graded to produce the
specified camber. The camber should be checked with the Camber Board at approx. 100 mintervals along the road. If the desired camber is not achieved, the process of grading should be
repeated.
After the correct camber has been achieved, rolling can start, commencing at the edge
towards the centre. The roller should progress section to section at the same rate as the Grader.
About 8 passes are generally required to achieve full compaction.
4.3.5. Use ofdust palliatives
4.3.5.1. The main disadvantage being cited against gravel roads, is the dust generation,
considered as a safety hazard and pollutant to the environment. Besides being a safety hazard, a
very significant implication of dust generation is the loss of fines from the surface gravel which
leads to increased gravel loss and consequently more frequent maintenance. If, however, the
generation of dust can be controlled, the expenditure on gravel road maintenance can be
significantly reduced.
4.3.5.2. There is a wide variety of dust palliatives available which can be divided into 7
basic categories, as under:
(a) Water
(b) Water absorbing products (hygroscopic)
- Calcium Chloride brine and flakes
- Magnesium Chloride brine
- Sodium Chloride (Salt)
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IRC:SP:77-2008
(c) Organic Petroleum Products
- Asphalt emulsion
- CutbackAsphalt (LiquidAsphalt)
- Dust oils
- ModifiedAsphalt Emulsions
(d) Organic Nonpetroleum Products
- Animal Fats
- Lignosulphonate
- Molasses/Sugar Beet
- Tail Oil Emulsions
- Vegetable Oils
(e) Electrochemical Products
- Enzymes
- Ionic Products
- Sulphonated Oils
(f) Synthetic Polymer Products
- Polyvinyl Acetate
- Vinyl Acrylic
(g) ClayAdditives
- Bentonite
- Montmorillonite
4.3.5.3. The selection of type has to be based on the quantity of fines in the surface
material, climatic conditions and traffic volume. The following four categories of dust
palliatives appear suitable for Indian conditions:
(I) Water
(ii) Water absorbing products (hygroscopic)
(iii) Organic petroleum products
(iv) Clay additives
4.3.5.4. Prior to applying dust palliatives, all the surface defects should be removed,
gravel added to provide the correct shape/camber/superelevation and the surface compacted.
The surface should be dampened (except when non-emulsified petroleum products are used).
The dust palliative should then be applied uniformly over the surface. After light compaction.
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IRC:SP:77-2008
traffic may be allowed ifchlorides are used while for other products, some time may be required
for the product to get absorbed before allowing traffic. Field trial sections need to be laid and
their performance monitored to evaluate the efficacy ofa product.
4.4. Maintenance ofShoulders, Drainage and Structures
4.4.1. Inspection of drainage system, shoulders etc. in both dry and rainy seasons is
necessary for effective identification of various defects. In the dry season, structural damages
can be better identified and in the rainy season, actual functioning ofthe drainage system can be
evaluated. Any field supervisor must evaluate the extent of damage in order to quantify the
needed maintenance measures; such an evaluation can best be done by inspection on foot. The
supervisory staffshould look for:
(i) Ditch cross-section destroyed
(ii) Ponding in the ditch and shoulders
(iii) Silting
(iv) Uneven ditch invert, varying x-section
(v) Invert and sides ofditch eroded
(vi) Drain destroyed
(vii) Ditch lining damaged
(viii) Ponding/erosion
4.4.2. Given below are the common defects, their causes and measures needed for
rectification:
SL.
NO.DEFECTS CAUSES
MAINTENANCEMEASURES
1. Ditch cross
section
destroyed
Plying of
vehicles/movement of
animals
Reshaping/ Regrading of
ditch
2. Ponding in ditch
and on shoulder
Insufficient ditch x-
section
Deepening of ditch
3. Silting of drain Water flows slowly on the
invert slope
Desilting of ditch
4. Uneven ditch
invert
Blockage caused by
debris/vegetation
Clearing, cleaning and
regrading
5. Erosion of sides
and bottom of
ditch
Too steep gradient Reinforcing of ditch slopes,
regrading or realignment of
drain, ditch checks
6. Destruction of
lined or precast
drain
Poor alignment or change
in flow direction
Erosion control and
realignment of drain
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IRC:SP:77-2008
7. Ditch lining is
damagedSettlement/erosion of soil
under ditch
Erosion repair and lining
repair
8. Ponding, erosion In-sufficient lateral
drainage
Provision of lateral drainage
9. Silting, blockage
by aebns oi
culvert
Too flat gradient, in-
conect positioning of
culvert, floating debris
lodged in culvert
Clearing and cleaning and
provision oi debris rack.
1 AlU. Erosion of
stieam bed at
culvert outlet
Water flow veiy
fast/culvert invert on a flat
grade
™ * .
Erosion repair
11. Settlement
cracks on the
culvert
Settlement of soil below If minor cracks, only repair
01 cracks. In case oi major
settlement, the culvert must
be reconstructed.
12. Rusting of steel
in culvert
Weathering, poor quality
material
Repair of steel section
13. Cracks in paved
surface of
causeways
Settlement Sealing of cracks
14. Obstruction on
shoulders
Operational Removal of obstruction
15. Level of
shoulders higher
than carriageway
Transportation ofcarriageway material byraflfic, swelling of soils,
vegetation growth.
Regrading of shoulders
and surface vegetation
control.
16. Ruts, depressions
or Inadequate
Cross-slope in
shoulder
Erosion, plying of vehicles Patch work, reshaping and
camber correction
17. High vegetation
on shoulderUnchecked growth of
vegetation
Vegetation control
18. Level of shoulderlower thancarriageway
Erosion/settlement of
carriageway
Replenishment of shoulder
19. Vegetation
overgrowth on
slopes
Lack of grass cutting,
trimming
Vegetation control
20. Erosion of slopes
due to surface
water
Rain water accumulation at
the toD of the sloDes
Erosion repair by cut off
ditch, collector drains,
chutes, berms, vegetation
cover and masonryprotection
Source : Document on Rural Road Development in India Vol. II, CRRI, 1990
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IRC:SP:77-2008
4.4.3. Activities
(i) Reshaping/Regrading/Deepening of Ditches/Drains: These can be donemanually. Alignment should be set by string line and the materials within the
string line should be cut and removed. Cross section, grading and depth should
be checked and corrected. Wherever possible, motor grader can be used for
these activities. The excess material must be removed from site and in no case
should be spread on the road surface.
(ii) Clearing and cleaning of Ditches/Drains: Any object which can interfere
with water flow should be removed. These objects should be disposed of well
away from the road so that these cannot impede the water flow again.
(iii) Repair of Drain Erosion: This should be done by replacing and back filling the
lost soil. Permanent measures like masonry lining or precast drain can beconsidered.
(iv) Repair of Drain lining: Settled or damaged precast sections or loose stone
should be removed and underlying soil compacted. After addition of fresh
soils, the levels should be corrected and then only fresh stones or precast drain
should be laid.
(v) Vegetation control: Except in arid areas, once a year, grass and weed cutting
and bush clearance on the shoulders is a must. In case of earth or gravel roads
these activities may be required to be done more frequently. Tractor-towed mowercan be employed where available, but ordinary manual method should be sufficient
for the purpose. Dead or leaning trees should be removed from the roadside. Use ofchemicals or burning of the roadside vegetation should be avoided as these are
harmfiil.
4.5. Special Problems ofHill Road Maintenance
4.5.1. Some ofthe special problems ofhill road maintenance are:
(1) Snow clearance
(2) Slips and landslides
(3) Drainage
Snow Clearance
The roads in the Himalayan hill region get covered with snow. Snow clearance can be
done manually or by special equipment (dozers, snow masters and snow blasts).
Landslides and Slips
Landslides and slips are a common feature of hill roads. Road maintenance in
areas subjected to landslides and slips poses severe problems. The greatest of
them is quick removal of debris and restoration of traffic. Mechanical equipment
like dozers becomes very necessary.
Drainage maintenance
Maintenance of drainage structures is an important task in hill road
maintenance. The quick and efficient removal of water prevents slips and
landslides and road deterioration. Drainage arrangements such as catchwater
74
IRC:SP:77-2008
drains, cross-drainage structures, side drains and subsurface drains should be
inspected before the monsoons and cleared ofall obstructions.
4.6. Maintenance Management
(a) General
The objectives of maintenance management are to plan and programme the
maintenance activities making optimal use of the resources of men, materials,
machinery and money so that the planned works are performed to a traffic-
worthy condition. The steps to achieve these objectives are discussed below.
(b) Road Data Banks
A proper management decision could be taken only when sufficient data are
available on the problem. Hence it is of vital necessity to collect and compile all
relevant data about the road and its environment and the resources available to
maintain the road network. These data should also be updated regularly. It is
reconmiended that the following data may be made available in the road data banks.
(i) Road cross-section including pavement composition (type and thickness),
shoulders, height ofembankment, side slope etc.
(ii) Geometries ofalignment
(iii) Details of various structures along the road viz., cross drainage structures,
roadside drains, breast walls, retaining walls, kilometre stones, traffic signs,
godowns etc.
(iv) Condition of the road-pavement surface condition (rutting, potholes etc.)
condition ofshoulder, and side drains.
(v) The maintenance history of the road - the date and type ofmaintenance put in
and its subsequent performance.
(vi) Traffic volumes and the quarterly rate and type ofaccidents.
Some of the road features are of a permanent nature like geometric design
features, cross-sectional details etc. and require to be updated only when there
is a major reconstruction. However, the road condition surveys (in terms of
PCI) and traffic counts etc. need to be updated at reasonable frequency. Each
State should possess a suitable machinery to collect, analyse and compile such
data which can be ofimmense use in maintenance management. A system of
road registers for each road can also be introduced.
(c) Standards of Maintenance
The next step in maintenance management will be to evolve reference standards
to help the maintenance staff to take the right decisions. In a systems concept,
there are three distinct types ofreference standards:
(i) Performance standards which define the level of quality below which the
various components ofthe road should not fall, so that the road users are given
a satisfactory level of service from the technical and economic points ofview.
These standards are the basis for determining when and what type of
75
IRC:SP:77-2008
maintenance activities are to be provided to the road network. Rutting,
potholing etc. are the parameters used to assess the performance level;
(ii) Quantity standards, which indicate the resources required to achieve the
necessary level ofservice; and
(iii) Operational standards, which specify the working method and crew
requirement consistent with a reasonable level of productivity for each
maintenance activity possible. These standards can be revised and improved
based on the achieved possible output in the field.
(d) Operational Management
For proper management of the resources allocated for maintenance, the objectives
to be aimed at should be reduction in costs for a defined quality ofwork, better work
performance within the same cost and proper deployment ofmen and machinery to
ensure an optimal utilisation of the available resources. For this, it is necessary to
identify the basic maintenance activities, quantum of work needed in relation to
road performance standards and the resources needed to fulfil these tasks in terms
of materials, machinery and man-hours. Having done this, it would be easy to
prepare a work schedule for weekly, monthly, quarterly and yearly operations. In
this way, it will be possible to move from a purely financial accounting system to a
rational process ofanalytical management.
Modernisation of maintenance management may involve radical changes in
traditional working methods. Mobile system of gangs in the place of the
time-honoured labour groups, who are practically immobile and have little or
no equipment will go a long way in streamlining the routine maintenance work.
The maintenance personnel should also be given periodic training.
A simplified Rural Road Maintenance Management System is given below
(Fig. 4.12).
Road Inspection and Road
Inventory
Data E
Condition Rating
Base
Traffic Data
Maintenance Budget
Rating Scale
Prioritization of
Maintenance Intervention
r
Annual Maintenance
Programme
Fig. 4.12 : Flow Chart for Rural Road Maintenance Management System
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IRC:SP:77-2008
(e) Condition Rating in Terms ofPavement Condition Index (PCI)
The most simple rating scale for the Pavement Condition Index, is roughly, derived
from the speed oftravel, as under:
Normal Driving Speed (km/h) PCIOver 35 5
25 to 35 415 to 25 3
10 to 15 2
Less than 10 1
Akematively, the riding comfort observed when driving at a design speed of 40
km/h can be assessed as under:
Riding Comfort at 40 km/h PCISmooth and Pleasant Ride 5
Comfortable 4Slightly Uncomfortable 3
Rough and Bumpy 2Dangerous 1
(f) Prioritization ofMaintenance Interventions
The following prioritization scheme for maintenance intervention may be adopted.
SI.
No.
Condition of Road PCI Type of Intervention
1. Ridability is very poor and the
surface is very rough and uneven
< 1 Reconstruct immediately
2. Ridability is poor and the surface
is rough and uneven
1 to 2 Regravel Immediately;
routine maintenance to continue
3. Ridability is fair with intermittent
rough and uneven sections
2 to 3 Regravelling within 1 year;
routine maintenance to continue
4. Ridability is good with a few
slightly rough and uneven sections
3 to 4 Routine maintenance
5. Ridability is very good <4 Routine maintenance
4.7. Organizational!Aspects ofMaintenance Management
It is necessary to have a suitable organisational set-up for an effective implementation of
various maintenance measures. There should be a separate maintenance unit for rural roads in
each district, to carry out the monthly maintenance work programme. Depending on the nature of
the maintenance activities, the work could be outsourced to local people. The required
77
IRC:SP:77-2008
implements/plant/equipment could be provided to the local contractors. Concerted efforts are
required to organise suitable training programmes for the staffofthe Maintenance Units and for
capacity building ofthe local contractors.
4.8. Do's and Don'ts
Do's Don'ts
1. Determine the cause of any surface defect before
taking any remedial action.
1. Do not undertake any maintenance
operations without Safety Measures at
2. During periodic maintenance and resurfacing work sites.
operations, restore the correct crossfall and 2. Do not attempt to compact fresh
sunerel evation giavci uy iiciiiic, wiiiiuui Using proper
3. Carefully select surface gravel to minimize dust compaction equipment.
nmn 1 ptti ^J. Do not overlook the maintenance of
4. Make all eiiorts to mamtam a good dramage system. me arainage system.
5. Scientifically decide upon the number of times
during the year that each unpaved road will need
grading, based on a range of factors.
4. Do not decrease or increase the
existing superelevation during
inainiendnce operdiions.
6. Retain superelevation on curves during maintenance
operations.
5. Do not disturb roadside vegetation
while carrying out various
7. Prefer simple maintenance equipment e.g, towedmaintenance tasks.
grader over a motor grader. 6. Do not decide upon the Dragging
8. Carry out a Condition Survey to determine PCI,frequency arbitrarily without practical
tests.atleast once a year, preferably twice, before and after
rainy season. 7. Do not ignore the maintenance of any
9. Adopt a systematic maintenance management system
as recommended in the Manual.
grass lining/ turfing provided to
control erosion.
10. Combine heavy grading with regravelling to restore
thickness of gravel surface.
8. Do not undertake any maintenance
task without considering the data
obtained during the last condition
survey.
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IRC:SP:77-2008
APPENDIX-A(Para 2.2.2.1 and 2.2.4)
PROPORTIONING DIFFERENT MATERIALS FOR ACHIEVING THEPRESCRIBED GRADING
A-1. Combining two materials
When only two materials are to be combined, a simple graphical methoddescribed below can be followed:
Steps:
It is required to blend sand (A) and silt-clay (B) to obtain the following gradation:
Sieve designation Percentage passing Material (A) Material (B)
4.75 mm 100 100
2.36 mm 80-100 91
1.18 mm 50-80 34 100
425 micron 30-60 10 84
300 micron 20-45 3 59
75 micron 10-25 2 36
(i) On a convenient size of rectangular graph, scale off top linearly from 100 to 0
as percentage of A in mix. Scale off the base corresponding from 0 to 100 as
percentage of B in mix. Scale off the vertical ordinate from 100 at top to 0 at
bottom on the left and 0 at top to 100 at bottom on the right, representing the
percentages passing sieve [Fig A-1].
(ii) On the left ordinate, mark off percentages passing the given sieves for material
A. On the right ordinate mark off percentages passing the given sieves for
material B.
(iii) For each sieve size, connect by a straight line the points, representing the
respective percentages passing each material. The intersection of each sieve line
by any vertical line will define the combined grading of the two materials mixed
in the proportions shown in the top and bottom horizontal scales.
(iv) On each sieve line, the specified percentage passing limits are marked by
small circles. The intercept lying between the circles represents, for any
particular sieve line, the range ofproportion that will comply the specification.
(v) If mixtures within the specification limits are possible, vertical lines can be
erected such that their intersection points with all sieve lines lie on the
acceptable intercepts. The highest and the lowest percentages of either material
at which this can be done represent the limiting mixtures which conform to the
specifications. The mid-point between the limiting mixtures will usually provide
the best mixture.
79
IRC:SP:77-2008
100
80
>60
Oz.
COV)
I-
oLUOL
40
20
80
PERCENT OF MATERIAL A IN MIX
60 50 40 25 20
1
1
1
9 7« mi^ -—1
- -
I
1
8
1
y\1
1 r\
^^^^1
1
32 40 60 74 80
PERCENT OF MATERIAL B IN MIX
100
Fig. A- 1GRAPHICAL METHOD OF COMBINING TWO AGGREGATES
(vi) In the limits indicated are (i) 68 per cent A, 32 per cent B and (ii) 26
percent A, 74 per cent B. In practice, the acceptable properties would lie in the
range of A:B=2:1 to A:B=1:3. Probably aratio ofA:B=1:1 would be the best.
A-2. Combining Three Materials
In dealing with mechanical stabilisation, it is often found necessary to combine
different materials to obtain the finally desired gradation. Rothftach's graphical
method is a reasonably quick, accurate and simple method, and is used, for design
of cement concrete mixes, bituminous mixes and granular mixes. The method
consists ofthe following stages:
(i) Using the desired aggregate gradation, a distribution curve is plotted with the
percentage passing as linear ordinates and the sieve sizes on the horizontal scale. In
order to mark the sieve sizes on the horizontal scale, an inclined line (OA in
Fig. A-2) is first of all drawn. By marking the known percentages passing each size
sieve on this line and dropping vertically the intersection point to the horizontal
80
IRC:SP:77-2008
axis, the location ofthe sieve size on the horizontal axis is determined.
(ii) The particle size distributions of the given materials to be blended are plotted on
this scale. The distribution curves will not generally be straight lines (Lines OB,CDE and CF GAin Fig. A-2).
mm mm mm mm mmSIEVE SIZE
Fig. A-2 : Rothfuch's Graphical Method of Combining 3 Materials
(iii) With the aid ofa transparent straight edge, straight lines are drawn representing the
particle size distribution in the best possible manner (Lines HJ and KA). This
means that the areas enclosed between the distribution curve and the straight line
should be minimum and are balanced about the line.
(iv) The opposite ends ofthese lines arejoined together (Lines BH and JK).
(v) The proportions for blending can be read offfrom the points where thejoining lines
cross the straight line representing the mixture. These points are L and M.
81
IRC:SP:77-2008
The method is illustrated by the following example
:
Cols. 1 and 2 in the Table below give the gradation limits for various sieve sizes of a
stabilized soil mixture. Three materials are available, whose gradations are given in Cols. 4, 5
and 6. Work out the blending proportion.
Blending of Materials
Percentage passing
Sicv6 Required
Gradation
Materials Available
designation Average CoarseSand
Local 47% A
Limits Aggregates(B)
Soil 49% B
(A) (C) 4%C
(1) (2) (3) (4) (5) (6) (7)
40 mm 100 100 100 100
20 mm 80-100 90 75 88
10 mm 55-80 67.5 20 62
4.75 mm 40-60 50 8 100 53
2.36 mm 30-50 40 6 80 42
600 mm 15-30 22.5 2 40 21
75 micron 0-10 5 Nil 2 100 5
A reference to Fig. A-2 will illustrate the stages involved in the graphical method. The
percentages ofvarious materials as scaled out are:
Material (A) : 47%
Material (B) : 49%
Material (C) : 4%
The gradation of the final mixture on the basis of above blending indicated in Col. 7 of
the Table.
A-3 Combining two Soils for Producing the Mix Meeting Require Dplasticity
Index
Two Soils A and B with Plasticity indices P^ & Pg can be proportioned to produce a
material having the required plasticity index P. Record the values of P^ and Pg at the top
ends ofacross, P at the crossing point. Determine the numerical differences P^-P and P - Pg. The
82
IRC:SP:77-2008
ratio in which the two soils should be mixed are indicated at the lower ends.
Mat . A : Mat . B :: P - Pg : - P
Example
:
The local soil-gravel in an area has a Plasticity Index (PI) of 30. Sand (PI = 0) is also
locally available from a nearby stream. What are the proportions in which the two can be
blended to obtain a PI of 1 0 in the mix?
Local Soil - Gravel p p
In the Mix, 1 0 parts ofLocal Soil - gravel (PI-30) need to be mixed with 20 parts ofSand (PI = 0)
from the nearby stream.
83
BIBLIOGRAPHY
1 Road Statistical Abstract 1999.
2. AASHTO Guide for Design of Pavement Structures,AASHTO 1993.
3. Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement
structures-Final Report Part 4 Low Volume Roads, prepared for NCHRP,Transportation Research Board USA, March 2004.
4. The Massachusetts Unpaved RoadsBMP Manual, 2001
.
5. Unsealed Road Manual, Australian Road Research Board Ltd., May 1993.
6. Document on Rural Road Development in India Vol. I, CRRI 1990.
7. Gravel Roads : Maintenance and Design Manual, US Department of Transportation,
Federal Highway Administration (SDLTAP), Nov 2000.
8. Grameen Sampark (Ministry of Rural Development) Vol. I, No. 4, Oct-Dec. 2005.
9. Document on Rural Road Development in India, Vol. II, CRRI, 1990.
10. IS:1498: Classification and Identification of Soil for General Engineering Purpose.
1 1 . MORD Specifications for Rural Roads, Indian Roads Congress, 2004.
12. Road Gravels, Compendium 7, Transportation Research Board ofUSA.
13. Unsealed Roads : A Manual of Repair and Maintenance for Pavements, National
Roads Board, New Zealand, 1986.
14. Overseas Road Note No. 31, TRRL, U.K.
15. Sudhir Mathur, S.K. Soni, AVSR Murty 'Use of Low-cost Agricultural Implements in
Low Volume Road Construction, Transportation Research Record, USA.
16. MORT&H Manual for Construction and Supervision ofBituminous Works, IRC, 2001
.
17. International Road Maintenance Hand Book Vol. II, Maintenance of Unpaved Roads,
PIARC, published by the Transport Research Laboratory, U.K.
18. Road Maintenance and Regravelling (ROMAR) Using Labour-based Methods, Hand
Book, by C.A, Anderson, A Beusch and Derek Miles, Intermediate Technology
Applications, 1996.
19. Dust Palliative Selection and Application Guide, US. Dept. of Agriculture, Forest
Service Nov 1999.
20. Jones D, Sadzik E and Wolmarans, I 'The Incorporation of Dust Palliatives as a
Maintenance Option in Unsealed Road Management Systems, 20* Australian Road
Research Board Conference, March 2001.
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IRC:SP:77-2008
21. Kadiyali Dr. L.R, and Lai, Dr. N.B "Principles and Practices of Highway Engineering,
Khanna Publishers, Delhi, Fourth Edition, Third Reprint 2006.
22. IRCrSP: 20 Rural Roads Manual, 2002.
23. IRC:SP:26 Report Containing Recommendations of IRC Regional Workshops on Rural
Road Development, 1984.
24. IRC:SP: 42 Guidelines onRoad Drainage 1994.
25. IRC:SP:48 Hill Road Manual, 1998.
26. IRC:36 Recommended Practice for the Construction of Earth Embankments for Road
Works.
27. IRC:37 Guidelines for the Design of Flexible Pavements, 2001.
28. IRC:34 Recommendations for Road Construction in Water-logged Areas, 1970.
29. Quality Assurance Hand Book for Rural Roads, NRRDA, Ministry of Rural
Development 2007.
30. IRCiSP: 72 Guidelines for the Design of Flexible Pavements for Low Volume Rural
Roads, IndianRoads Congress, 2007.
31 . PMGSY Operations Manual, National Rural Road DevelopmentAgency, 2005.
32. Overseas Road Note 1, Maintenance Management for District Engineers, TRRL, UK,
1987.
33. Overseas Road Note 2, Maintenance Techniques for District Engineers, TRRL, UK,
1986.
85
(The Official amendments to this document would be published by the IRCin its periodical, 'INDIAN HIGHWAYS', which shall be considered as
effective and as part of the code/guidelines/manual, etc. from the
date specified there in)